How do you calculate the full cost of a 200 m² trapezoidal steel roof covering?

This is a simplified geometry without roof valleys and dormers. For a more complex roof, the cutting layout must be prepared separately for each section. A triangular offcut cannot always be used on the other side. The profile direction, overlap and coating limit the possibility of rotating sheets.

For the example T35 with a cover width of 1.035 m, you need 20 strips per roof slope. Nineteen would give only 19.665 m. Twenty covers 20.70 m before final adjustment. For two slopes, you order 40 sheets of 5 m length, provided the project does not require a different solution.

The area according to cover width is 40 × 5 × 1.035 = 207 m². For this variant, the overall width of 1.082 m gives 216.4 m² of material calculated by full width. The price must indicate which area it refers to. The two units must not be mixed.

The sheet length in this calculation does not determine the support spacing. A five-metre section may require several points of support. Their number and position result from the verification of the profile and loads. Commercial dimensions do not replace roof calculations.

At the agreed rate of €11.11 net per m² of covering, the sheets cost 207 × €11.11 = €2,299.77 net. If the same figure of €11.11 meant the price per m² of the total, the result would be €2,404.20 net. The difference of €104.43 arises solely from the basis of calculation.

A reliable quote must also specify the steel thickness, coating type, colour and any fleece. Do not compare this calculation with any sheet described as T35. The profile height designation does not guarantee the same width or other parameters.

In our exercise, let us assume €555.48 net for the processing and €208.30 net for the fixings and other small components. These are assumed amounts, not universal surcharges. In a real order they arise from the edge lengths, the details and the fixing design.

Calculate flashings for the eaves, ridge and sides of the roof slope. Check penetrations and the junction with a higher wall separately, if present. Two roofs with the same area can have a different perimeter. That is why simply multiplying metres by one percent of additions can be misleading.

Let us further assume €1,805.31 net for the installation, €254.59 net for the equipment and €219.88 net for the delivery. The full total of the example is €5,343.33 net. This gives €26.72 net per square metre of actual roof area. The result covers the items described, not the entire roof construction.

New structure, insulation, replacement of damaged substrate and installations are not included here. Tax depends on the conditions of the given transaction. In the quote, check whether unloading and work protection are already included in the price. Do not assume they are present without a written note.

The building height, access and number of obstacles on the roof slope matter. Work on an occupied building may require a different organisation. Shorter sheets increase the number of transverse joints. Longer ones require appropriate handling and space for unloading.

The profile and thickness are selected according to loads and supports. Do not reduce them merely to stay within the example budget. The steel sheet must correspond to the design. The cost of any additional purlin must also be calculated if you compare two structural solutions.

Give all contractors the same geometry and specification. Ask for material, additions, labour and logistics to be separated. Mark existing and new elements. This lets you see whether a lower total results from a better price or from omitting part of the works.

Finally, check quantities and units as well as the allowance resulting from cutting. Keep a reserve for identified risks rather than an arbitrary percentage without purpose. After measurement and inspection of the roof, the preliminary cost estimate can be turned into a specific order scope.