How to estimate the full cost of a roof
Costs and contracts
To budget for a roof, start with the sloping area on the drawings and work out how many sheets the layout requires. Include the timber or other supports, underlay, flashings, drainage and labour. A price per square metre can refer to the gross sheet area or to the area covered after side laps. Establish that basis before comparing quotations. At valleys and dormers, the cut pattern affects how much material you buy. Delivery, unloading and, on a refurbishment, stripping the old covering can also change which quotation gives the lowest cost for the finished roof.
Which area should you measure first?
Convert the dimensions on the floor plan to the actual sloping dimensions. Include overhangs, dormers and projections beyond the walls. Measure each plane of a simple roof separately. For a more complex shape, use a quantity take-off and a sheet layout.
Allow for overlaps and for cutting at valleys and hips when calculating the ordered quantity. A gable roof and a roof with several dormers can have similar areas and very different waste allowances. Work out waste from the actual layout.
What is an effective square metre?
Overall width includes the full sheet. Effective width is the width remaining after the side lap. A lower price per gross square metre may produce a higher roof total. Convert both prices to the same basis before comparing them.
One T18 profile is 1,142 mm wide overall and covers 1,100 mm. A 4 m sheet provides 4.4 m² of cover before any end lap. Its gross area is 4.568 m². Other T18 profiles may have different widths.
For a price per linear metre you also need the cover width. At 1.10 m effective width, one metre of length covers 1.10 m². Make this conversion before comparing prices. State the piece count and lengths on the order.
How should you itemise a roofing quotation?
List the covering, structure and layers beneath the sheet separately. House roofs often need battens, counter-battens and an underlay. A heated loft also requires suitable insulation and airtight connections on the inside. Eaves and roof windows need their own details whatever insulation is chosen.
Measure ridges, eaves, verges and valleys for flashings and accessories. Add chimney flashings, service penetrations, fasteners and seals. List gutters, downpipes and roof access equipment separately so omissions are visible.
How can you use a catalogue price?
A Polish price list effective from 28 October 2026 gives a 0.50 mm polyester-coated T18 sheet at approximately €8.42 per effective m² excluding VAT, or €10.36 including the list’s 23% VAT. For 100 m² of cover, the converted material total is about €1,035.57 including VAT, before waste or other roof components. Rounding the converted unit prices can give a slightly different total.
Use the dated list to understand the calculation. For a purchase, obtain a quotation for the actual coating, colour, length and quantity. Discounts affect sheet prices, while delivery and unloading still have to be paid. Compare totals with all applicable supplements.
What should installation costs cover?
Ask whether labour covers substrate preparation, membrane installation, flashings and gutters. On a refurbishment, allow for removal, waste handling and temporary rain protection. Agree how extra work will be priced if damaged timber is found after stripping.
Building height, chimneys, access and scaffolding affect labour. Define scope, sequence and acceptance in the contract. Compare quotations on the same basis so the cost of laying sheets alone is identifiable within a complete roof price.
How do you prepare a budget for ordering?
Get at least two quotes against one schedule. Keep steel thickness, coating and flashings comparable. Record the unit, quantity, net and gross prices for each item. Check quotation expiry and how sheet length or the number of unloading stops affects delivery costs.
Set the contingency to suit the project. A well-specified new roof has different uncertainties from an existing frame that can only be inspected after opening. List the likely extras. The completed estimate should give the cost of a watertight roof ready for handover.
Agree how surplus sheets will be settled and whether missing elements can be ordered later.
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What to include in your enquiry
Tell us how you plan to use the material, the dimensions and the quantity you need. Include the thickness, grade or variant name, along with the delivery town or your preferred collection branch. For a specific product, add its name or a link to the product page. We will reply to the email address you provide to discuss availability and the terms of your order.
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