The roof shape should be chosen mainly for how the loft will be used and how simple the details will be, not for the name of the form alone. It is worth checking how many slopes, hips and valleys the planned footprint will create, and how that affects flashings and drainage. A simple duo-pitch roof makes the water flow easier to read and the sheets easier to lay out, while a more complex geometry demands more careful drawings. The final choice of covering and layers should be left to the designer, as angles, supports and details decide it.

Roof battens form the framework that supports the covering and mark where sheets are fixed, so before buying material it is worth agreeing with the contractor whether their spacing and cross-section match the geometry of the chosen profile and the expected loads. An even-looking finished frame is not enough — batten positions must suit the shape of the ribs, and for trapezoidal sheets the support method follows from the design and the tables for the specific profile. Also check that battens are not confused with counter-battens, which create a ventilation gap above the underlay.

First establish whether the old sheets contain asbestos and plan their safe removal — only then choose the covering. The key variable is the condition of the roof structure, not just the weight or price of the new material. Check rafters, purlins, wall plates and connections, especially near chimneys and former leaks; do not judge the load-bearing capacity of the timber from a photograph. The colloquial term “eternit” is used for various sheets, so determine the covering’s composition from documentation and expert assessment. Before setting a date, ask your municipality about collection rules and possible support. Only after these steps should you compare trapezoidal sheet with modular metal tile.