First establish whether the building will be heated continuously, periodically or not at all, as this determines the choice of envelope. Also check the working temperature, humidity, substance emissions and the method of cleaning the interior. A dry warehouse, a workshop and a facility with frequent interior washing place different demands on the building envelope, and universal sheeting in an attractive colour need not withstand an aggressive environment. A sandwich panel combines facings with an insulating core and reduces the number of successive operations, but the benefit depends on preparation of the structure and delivery of components in the correct sequence.

Before comparing the cost of metal sheeting with other roof coverings, decide whether you are choosing a variant for the whole roof or only part of the slope — this determines the scope of the estimate. Check that the offers cover the same drawing, actual dimensions, pitch, valleys, dormers, chimneys and windows, and how the loft will be used. For a renovation, first assess the condition of the structure, as repairs and dismantling depend on it. Only then compile complete amounts including substrate, flashings, transport and installation, on the same net or gross basis.

A price enquiry for ‘100 metres of steel sheet’ needs clarification. One hundred square metres of roof surface is not the same as one hundred linear metres of sheet. The quote also requires the cover width, the lengths and the billing method. The example below shows the calculation for a simple roof with an actual area of 100 m². A square metre describes an area. A linear metre means the length of material at a specified width. If a sheet covers 1.10 m, then 100 linear metres corresponds theoretically to 110 m² of coverage. This does not yet indicate how that length is to be divided between roof slopes and overlaps.