The roof shape is chosen primarily to suit the building's form, the attic's needs and local provisions, not the covering alone. It is worth checking whether the chosen arrangement of slopes allows the interior and drainage to be planned sensibly. A simple gable roof may be clear in structural terms, but it is not always the cheapest in every project. With a mono-pitch roof, water runoff and wall heights must be assessed. For a usable attic, the cross-section of the rooms is key, not the floor area alone.

The full roof build-up is determined not by a single material but by the arrangement of layers under the covering, which provide support, protection against water, reduced heat loss and moisture control. Before buying, establish the complete cross-section with the function of each layer and the detailing at the eaves, ridge and openings, rather than selecting materials separately. Check that the instructions permit their combined use and whether a layer correct under one product will suit every product. Remember that the membrane does not replace the vapour barrier, and the anti-condensation fleece is not insulation.

Begin by establishing whether the old sheets actually contain asbestos, rather than judging them by colour and shape. If documents are missing, agree the identification method with the relevant authority and a contractor; do not take samples by breaking or drilling yourself. At the same time, assess the condition of the roof structure and the geometry of the slopes, since some problems only become visible once the sheets are removed. The choice of new covering — trapezoidal sheet or metal tile — depends on pitch, structure and building function. Also plan the safe removal of the old material and check with the municipality whether asbestos support covers only dismantling, transport and disposal.

Choose the covering to suit the roof pitch, the building structure and the way the building is used. Tile-effect metal roofing, trapezoidal steel sheet and insulated sandwich panels serve different functions. What matters is the cost of the whole roof build-up, as well as appearance, acoustics and the possibility of repair. Colour or the price of a single sheet is not enough. First check the design requirements, then compare the solutions approved for the given roof slope. Start with the pitch and dimensions of the slope. Every product has its own range of application. Tile-effect metal roofings come with different minimum pitches, so the parameter of one model does not apply to the whole group. At a low pitch, the laps, flashings and the method of water drainage become particularly important. The product data sheet and the installation instructions must be consistent with the design.