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.

Before choosing a covering, decide whether the cabin will be used only in summer or also in winter — this is the first question before making a decision. The answer affects the layer arrangement, ventilation and the risk of condensation. Check whether a simple T18 or T35 trapezoidal profile suits the structure, and whether a modular metal tile suits a more residential form. Consider rain noise, pitch, batten spacing and site access. Remember that the metal sheet alone does not solve temperature and moisture issues.