The choice of roof covering depends primarily on the roof pitch, the load-bearing capacity of the structure and the intended use of the house. Before buying, compare the project requirements with the parameters of the specific product, including the minimum pitch, permissible loads and details at the eaves and ridge. Check whether a lighter material still requires the roof truss to be assessed by a structural engineer. Only after these determinations should you choose the pattern and colour, bearing in mind that metal roof tiles, trapezoidal sheeting and sandwich panels serve different functions.

You can recognise a roofer to whom a difficult roof can be entrusted by how they prepare and carry out the work, not by a photograph of the finished slope alone. Before deciding, check whether they can point to the instructions for the chosen covering and explain which drawings apply to your roof, and ask about projects with a similar geometry and type of covering. Ask also how they document the stages that will be covered and how they report problems with the substrate. Questions about details at the chimney, valley and eaves will tell you more than a general view of the building.

The covering that places the least load on the structure is the one with the lowest mass per square metre of finished roof surface, not per individual sheet. When choosing, check whether the stated value refers to the covering area and what purlins and additional layers are required. It is also necessary to establish where these loads act and how they reach the walls. A comparison made for the same roof area avoids a misleading impression of lightness. Final design decisions remain with the structural designer.

A multi-pitched roof is a form with several connected slopes, and the choice of covering depends primarily on the geometry and sheet layout rather than on the name alone. Check the detailed drawing of ridges, hips and valleys, along with a cutting plan for the sheets, to assess waste and how details will be formed. For metal roof tiles, T18 or T35, analyse the pitch of each slope, ventilation continuity and drainage. The suitability of a given format should be decided by a full schedule of material and works, left to the designer.