What budget should you allow for covering a 200 m² roof with trapezoidal steel sheet? A worked example

This is a model for calculation. On a real roof, the terminations at the eaves and ridge must be taken into account. The sheet length is confirmed once the details have been established. The design also specifies the profile, thickness and supports. The calculated area does not mean that any trapezoidal steel sheet will be suitable.

Let us assume a coverage width of 1.10 m. For an eave of 20 m, this gives 18.18 strips, so 19 sheets are needed on one roof slope. Two slopes require 38 pieces. Each sheet with a length of 5 m provides 5.5 m² of coverage. In total, the ordered elements give 209 m² of coverage before cutting.

If this variant has an overall width of 1.137 m, the full sheet area will be 216.03 m². This is another correct figure, but for a different unit of price. It must not be added at the same time and then a general percentage added again for the same laps.

Assume €11.11 per m² of effective cover before VAT. The purchased sheets give 209 m², so 209 × €11.11 comes to €2,321.99 before VAT. This illustrative rate is neither a supplier quote nor a market average.

When the quote gives a price per overall metre, 216.03 m² and the appropriate rate for that unit must be used. Amounts per effective metre and per overall metre are not interchangeable. Before comparing two proposals, it is necessary to check how the basis of settlement has been described.

The add-on amounts are hypothetical cost-estimate items. This model has no new structure, insulation, gutters or removal of the old roof. If these are needed, they must be added separately. The total must not be treated as the price of a complete building.

The area does not describe the length of edges or the number of details. A roof with many slopes may require more cutting and longer work. Chimneys, vents and junctions with a higher wall change the scope of flashings. Differences may also concern access and the method of delivering material.

The height of the building and the load conditions affect the structure and the fixings. A comparison with a small garage of similar floor area need not be accurate. The quote should cover a specific building. The question about a rate “for laying 200 metres” alone leaves too many unknowns.

First refine the cutting plan and the list of add-ons. Limiting accidental over-ordering reduces delivery costs. It is worth comparing matching variants of coatings and profiles if the project permits a choice. Savings should not be made by arbitrarily reducing the number of supports or fixings.

Also check the delivery date against site readiness. Long storage of inadequately protected packs can lead to damage. A cheaper purchase will not pay off if part of the material has to be replaced. In the budget, allow for the real organisation of works, not just the invoice price for the steel sheet.

Before placing the order, it is worth establishing the route for moving material onto the roof. Even a simple cutting plan may require additional equipment if the access is narrow or there is no space to set down the pack. The stated 200 m² does not describe these conditions. Agreeing the organisation helps avoid a situation where paid-for sheets wait for the next installation date and a separate crew visit.

Replace the assumed dimensions with the actual drawing of the roof slopes. Enter the coverage of the selected profile and calculate full strips. Separate the roof area from the quantity of material purchased. Then add flashings, accessories and the scope of work. Each item should have a clearly described unit.

When approving the price, check whether the total is net or gross and what elements it includes. Establish unloading and responsibility for measurements. A well-prepared schedule allows offers to be compared without guessing. It also provides a basis for checking the completeness of delivery and settling the works performed.