Beginner’s Guide to Metal Roof Sheets

Planning a new roof for your warehouse, carport or agricultural building? Metal sheets are a smart, long-lasting option - but with so many profiles, coatings and add-ons to choose from, it’s not always clear where to start.

This guide covers the key things you need to know:

• What corrugated and box profile mean - and how they differ
• What terms such as 32/1000 and plastisol-coated steel refer to
• When it’s worth adding anti-condensation backing
• What’s involved in fitting metal sheets yourself

If you’re weighing up your options or wondering what to look out for, you’ll find everything here to get started with confidence.

In this article:

Corrugated v.s Box Profile - What's Right for You?

How are metal roof sheets measured?

• Corrugated sheets short summary
• Box profile sheets short summary
• Quick compare - corrugated v.s box profile

Polyester vs Plastisol - Which Metal Sheet Coating is Better?

• Common questions
• Galvanised sheets

What are Anti-Condensation Sheets & do I Really Need Them?

What Metal Roofing Type is Best for my Project?

• Can I Install Metal Roofing Myself?
• What’s involved
• Useful tools
• Accessories & fixings you’ll need

A Few More Questions to Help you Decide

Corrugated vs Box Profile: What’s Right for You?

Metal roof sheets come in two main shapes or profiles - corrugated and box profile. Both are strong, weatherproof and commonly used on sheds, garages, carports and lean-tos. But they have different looks, strengths, and often, measurements. So, to avoid confusion let’s start with the basics so we know what we’re comparing with what.

How Are Metal Roof Sheets Measured?

Before comparing profiles (the shape or pattern of the sheet’s surface), it’s worth understanding how metal sheets are sized:

• Overall width is the full edge-to-edge width of the sheet.
• Cover width is the usable width after overlaps are accounted for. This is the number you’ll use when working out how many sheets you need.
• Cover length is the same idea as above - whilst most sheets are made to standard widths, you may find that sheets are available in both custom and standard lengths.

All metal sheets are designed to be installed with a slight overlap. This ensures rainwater doesn’t get through the joins. That overlap is why cover width/length is always smaller than the full sheet and is the one you’ll want to check before you buy.

Corrugated Sheets - A Quick Summary

Corrugated metal sheets have a regular wavy pattern and a more traditional appearance. They’re lightweight, easy to handle, and often used on sheds, lean-tos and small timber-framed roofs.

You’ll often see them labelled with numbers such as 13.5/3, where:

• 13.5 = the number of corrugations (raised wave sections) across the width of the sheet.
• 3 = the distance between the peak of each wave, in inches.

You will then also probably see the dimensions listed in metres and millimetres - just to shake things up! An example of a standard size:

• Overall width: approx. 1220mm
• Cover width: approx. 990mm (after overlap)

Corrugated sheets are a popular choice for a wide range of projects but they’re especially popular on larger agricultural buildings and warehouses etc.

Box Profile Sheets - A Quick Summary

Box profile sheets have a more angular shape, with flat sections and raised ridges known as ribs. These ribs add strength and rigidity, making box profile a good option for garages, workshops and wider roof spans.

Common profiles include 32/1000 or 34/1000, where:

• 32 or 34 = the rib height - the distance from the flat section to the top of the ridge, in millimetres.
  
• 1000 = the cover width, also in millimetres (1 metre)

Standard sizing example:

• Overall width: approx. 1070mm
• Cover width: 1000mm (after overlap)

The flatter sections between ribs also help water drain efficiently down to the eaves.

Choosing Between Corrugated and Box Profile

Factor	Corrugated	Box Profile
Look	Traditional, softer lines	Modern, angular finish
Feel	Strong but better suited to smaller spans or closely spaced supports	High strength, handles larger spans and exposed locations well
Typical uses	Barns, lean-tos, older stables, small utility shelters	Garages, workshops, carports, modern agri or commercial builds
When it makes sense	Smaller spans or when looks matter more than strength	Longer spans, visible roofs, or when strength is key

Both profiles are tough and resilient, easy to work with and suitable for light DIY jobs as well as heavier-duty commerical and agricultrual projects. The choice will come down to the finish you want, the size of the job - and budget.

Polyester vs Plastisol - Which Metal Sheet Coating is Better?

The basic construction of a metal roof sheet is obviously vital, but the coating is also important for protecting the steel underneath and an additional point to consider before buying.

Most metal sheets come with a polyester or plastisol finish. Both are protective, but each suits different project needs. Here's how they compare:

Feature	Polyester-Coated	PVC Plastisol-Coated
Finish	Smooth, painted surface	Textured outer layer (often leather grain-style)
Durability	Good for most DIY or garden builds	Longer-lasting, better suited to heavier use
Scratch resistance	Prone to light marking during handling or fitting	Tough outer layer resists scuffs and scratches
Appearance over time	Can fade slightly in direct sun	Strong colour retention and weather resistance
Best for	Sheds, lean-tos, small outbuildings on a budget	Garages, workshops, larger or more visible roofs
Cost level	Lower - a good balance of cost and performance	Higher - a longer-term finish with less maintenance

Common questions about finishes

Do plastisol sheets look plastic?

They usually have a textured, slightly matte finish - not cheap or synthetic-looking. Plastisol is often chosen for its ability to hide marks and blend well with timber or modern cladding.

Is polyester fragile?

Not at all - but it can scratch more easily during handling. Care during installation goes a long way.

Is plastisol worth the extra cost?

 If the roof is in a visible location, needs to last for 15+ years, or will take regular wear (like from tree branches), plastisol often pays for itself in durability.

What About Galvanised Sheets?

Galvanised sheets are finished in zinc but left unpainted - giving a plain silver-grey appearance. While they don’t offer the colour choice of coated sheets, they’re still:

• Tough and rust-resistant, thanks to the zinc layer
• Cost-effective for larger or low-visibility builds
• Ideal for utility spaces, farm buildings, animal shelters, or where airflow and strength matter more than finish

They may dull slightly over time, but they won’t peel or flake - and they’re often chosen specifically for their clean, simple look.

For practical, hard-working structures, galvanised sheets offer reliable protection without the extra cost of decorative finishes.

What are anti-condensation sheets & do I really need them?

If you thought anti-condensation sheets might just be a gimmick - you’d be wrong! If you’re roofing an enclosed, uninsulated space - especially a larger building, it’s important to think about condensation before you fit the sheets.

Even if the roof’s watertight from above, moisture can build up underneath. When warm air inside hits the cold metal surface, water droplets form on the underside - and over time, that can lead to drips, damp patches or even mould and rot in the structure below.

What anti-condensation backing actually does

Some metal sheets come with a special lining on the back that’s designed to absorb moisture before it turns into drips. It holds the water temporarily, then releases it gradually back into the air as the temperature rises (as long as there’s some ventilation).

You might want to consider it if:

• You’re storing tools, timber or anything else sensitive to damp
• The building’s enclosed and not insulated
• You’d rather avoid dealing with internal drips later on

It’s not something you’ll usually need for open-sided roofs like carports or for well-ventilated structures where air can circulate freely.

What about DIY alternatives?

Anti-condensation backing is factory-applied before the sheet is formed - so once the sheets are made, you can’t add it later. If you’re not going for this option, standard prevention methods like insulation, ventilation and moisture control can still do a lot to reduce condensation risk.

Some people look into makeshift alternatives - like lining the roof with felt or other absorbent layers - but these rarely match the reliability or low-maintenance benefit of a proper backing.

If you expect condensation to be a problem, it’s usually easier to tackle it from the start than try to fix it afterwards.

Which Metal Roofing Type Is Best for My Project?

Both corrugated and box profile metal sheets can be used across most projects - but depending on the size of the structure and the finish you're after, one may be a better fit than the other.

Here’s how they compare across common applications:

Project Type	Corrugated	Box Profile
Barns & Stables	Common in rural settings. Offers traditional agricultural styling.	Stronger shape holds up better on wider spans or exposed sites. Often chosen for modern agri builds.
Warehouses & Units	Can be used on smaller or secondary buildings.	More typical. Clean finish and high strength suit larger commercial structures.
Workshops & Garages	Works on simple timber frames, but may lack stiffness for insulation or interior lining.	Rigid, low-maintenance, and easier to insulate. Preferred for workshops or garages with regular use.
Carports & Lean-tos	Suits simpler designs or where appearance matches existing buildings.	Good for open-sided builds where strength, water run-off, and lifespan matter.
Sheds	Can work for basic sheds, but may be heavier and more costly than needed.	Sometimes used on larger sheds, but alternatives (bitumen, plastic) are often more practical.
Garden Offices	Rarely used — can be noisy and hard to insulate.	Only suitable with proper insulation and soundproofing. Not a first choice for most setups.
Open Shelters	Cost-effective and flexible. Used for log stores, bin covers, etc.	Also suitable. Often chosen based on availability or appearance.

In short, either profile can work for most builds. If your structure is large, exposed, or needs a cleaner finish, box profile offers more strength and stability. If you're working on a small outbuilding with a simpler frame or want a more traditional look, corrugated may be the better fit.

Can I Install Metal Roofing Myself?

Metal roof sheets are one of the more DIY-friendly options on the market - especially for smaller buildings like sheds, garages, or lean-tos. They’re lightweight, can often be cut to length and quick to install. But like any roofing job, it’s worth knowing what’s involved before deciding whether to take it on yourself.

What’s involved?

For most builds, you’ll need to:

• Fix timber battens or purlins across the roof frame
• Lay and overlap the metal sheets (usually side-by-side and sometimes end-to-end)
• Cut sheets to fit around edges, vents, or tricky roof shapes even if they’ve been supplied cut-to-size
• Secure everything with the right roofing screws
• Finish the edges and top with trim pieces like ridge caps and barge boards

If you’ve got basic tools and a good ladder setup, many homeowners and non-roofing-specialist tradespeople can take this on, expecially for smaller projects. But you’ll likely need a second pair of hands to safely move and position the sheets - and always take extra care when working at height. 

Tools You’ll Likely Need

• Cordless drill or driver – to drive roofing screws through the sheet
• Tin snips or a metal-cutting circular saw – to trim sheets if needed
• Tape measure and chalk line – for marking straight lines and fix points
• Safety gear – gloves (sheet edges can be sharp) and eye protection
• Ladder or scaffold – depending on roof height and access

What Else Will I Need?

To finish the job properly, you’ll also need a few extras beyond the sheets themselves. These make the roof weatherproof and secure and give it a clean, finished look.

Item	What it’s for
Roofing screws	Special screws that fix the sheet into the timber or steel frame. They come with a rubber washer to seal around the hole and stop water leaking through.
Ridge caps	If your roof is pitched (has two sloping sides that meet in the middle), a ridge cap covers the join at the top and stops water getting in along the peak.
Barge boards	These metal trims seal the side edges of your roof, protecting against wind and rain and finishing the roof neatly.
Foam fillers	These sit under the sheet at the eaves to fill the gaps in the profile shape. They block draughts, insects and rain being blown in underneath.

Most small roofs will need screws, ridge caps, barge boards, and fillers as a minimum. If you’re unsure, it’s always worth checking what your structure will need before ordering.

A Few More Things to Help You Decide

Still deciding whether metal roof sheets are right for your project? Here are a few questions people often ask us before they get stuck in, especially if it’s their first time working with this kind of roofing.

Do I have to cut the sheets myself?

Not necessarily. Most metal sheets are available in a range of lengths - and many suppliers (including us) offer cut-to-size options. That means you can order exactly what you need, which saves time on site and cuts down on waste. It's likely a small amount of trimming may still be needed to tidy things up or account for tricky shapes, this is usually done with tin snips or a circular saw and a suitable blade - just be careful around the edges.

Will it be noisy in the rain?

Metal sheets can be noisy in the rain, especially on uninsulated roofs like garden sheds or garages. If you’re concerned about noise, anti-condensation backing can help soften the sound — or you can add insulation underneath once the roof’s fitted.

Do I need anything underneath the sheets?

 In most cases, no. Metal sheets are often fitted straight onto timber battens, especially on outbuildings. Some people choose to add a breathable membrane for extra protection, but it’s not essential for a typical DIY shed or garage roof.

Are these sheets likely to rust?

 No - not if they’re installed properly. All coated metal sheets (whether polyester, plastisol or galvanised) are designed to resist corrosion. As long as the surface isn’t damaged during fitting and the overlaps are sealed correctly, they’ll hold up well for years.

Do I need planning permission?

It will depend on your project. Most small outbuildings fall under permitted development but if you’re building close to a boundary or making major changes, it’s worth double-checking with your local planning office. If in doubt, always check.

Is this something I can actually do myself?

 For smaller builds like sheds or lean-tos, absolutely. The sheets are generally easy to handle and as long as you’ve got the right tools - and maybe someone to help hold things steady - it’s a very doable job. Just make sure you’ve got all the bits: fixings, ridge caps, barge boards and anything else your structure might need.

Final Thoughts

Metal roof sheets offer a practical, cost-effective solution for all kinds of projects - from garden sheds to larger outbuildings. This guide has walked you through the key things to know - from profiles and coatings to installation basics and real-world use. Whether you're comparing materials or starting to plan your project, you're now in a better place to make the right call.