After winter, examine the sheet-metal covering, flashings and drainage before deciding the roof is watertight. Start with safe observations from ground level and from inside the building. Damp marks in the attic, a bent gutter or a displaced component call for the cause to be established. A wet patch does not always mean a hole in the metal — condensation or a blocked outlet may be responsible. Repair should therefore follow diagnosis, and inspection of the roof slope and fixings should be left to a suitably prepared specialist.

Choosing a metal roof for a modern company building depends primarily on how the interior will be used, not on the appearance of the covering alone. An open shelter needs a different approach from a heated warehouse, and a heated warehouse needs a different approach from an office. It is therefore worth checking the temperature and humidity inside and the type of business activity, because the roof must suit conditions on both sides of the building envelope. Define acoustic and fire requirements straight away, together with any equipment planned for the roof, such as ventilation units or photovoltaic installations. A project covering these elements from the outset makes installation easier and allows sensible placement of penetrations, skylights and service routes.

Rafter dimensions are determined by calculation, not by the building width alone. The span between supports, spacing of adjacent rafters, timber grade, loads and connection type all matter. Lightweight metal sheeting reduces the roof's self-weight, yet snow and wind still act on the structure. Price depends on volume, length and timber preparation. The order should match the design and the actual roof layout. A rafter works over the section between supports, carrying loads from the roof area assigned to it. The length of that section matters, not just the total beam length. An additional purlin can alter the structural behaviour, as can the spacing of neighbouring rafters.