The cost of a roof is best calculated in separate parts rather than by multiplying the covering price by the floor area of the house. To obtain a reliable estimate, you should prepare a plan of the roof slopes with dimensions and pitch angles, and for a renovation take into account the actual shape of the structure. In the material cost estimate, it is worth separating the covering area from the area of purchased sheet metal, because waste depends on the layout of the slopes and the length of the sheets. The final result is also shaped by flashings, insulation, access to the building and the scope of work. When comparing quotes, check whether they cover the same scope and unit of measurement.

A complete roof is a system comprising the load-bearing structure, protective layers, covering, drainage and essential accessories, not just the sheets themselves. When comparing cost, it is therefore worth checking whether the offer includes all these elements and their mutual compatibility. The key decision variable is the scope of the entire system: from a structure capable of carrying all anticipated loads, through layers with appropriate diffusion resistance and unobstructed ventilation, to flashings and fixings. Only a full list of elements with quantities and units allows you to judge whether two similar amounts relate to a genuinely comparable scope.