To correctly estimate the weight of T18 or T35 trapezoidal sheet, you must first establish which surface area the given unit mass refers to. Check whether the product data sheet states kilograms per square metre of covering or per square metre of the sheet's total area – these two values lead to different results. The designations T18 and T35 describe profile families, not one identical product, so weight can vary with steel thickness and geometry. To calculate delivery weight, sum the weight of all sheets according to their actual dimensions, then add the weight of packaging and accessories.

In Poland, the price of T18 and T35 trapezoidal sheet depends primarily on the specification, not on the profile name alone. When comparing quotes, check whether the rate refers to a gross square metre or a square metre of coverage, and whether it includes tax. Ask for the total price of sheets, accessories and delivery. Remember that a wider sheet has a smaller effective coverage width, so two prices per square metre may describe different quantities of finished roof. Leave the choice of profile and support spacing to the designer.

T7 is a low profile that can look good on soffits and small cladding. Its advantage is the subtle surface pattern. However, it should not be treated like a taller trapezoidal roof sheet. The choice depends on the intended use of the specific variant, the support and the dimensions of the area. Calculations must use the coverage width, not the full sheet width. For example, a sheet with a 7 mm profile has an overall width of 1195 mm and an effective width of 1155 mm. This means that after joining adjacent strips you will not get the full 1195 mm from each piece. The usable dimension takes account of the joint geometry. Another T7 variant may have different values.