The budget for a panel roof should be drawn up together with the support layout and the setting-out. The price per metre of panel will not show the cost of flashings, lifting or service penetrations. It is worth calculating the entire roof-closing stage. This way the order will match the finished structure and the actual organisation of works. The dimensions of the roof slopes, the pitch and the purlin spacing are needed. Include the locations of rooflights, roof hatches and equipment. Each of these elements may change the support or the scope of flashings. For an existing roof, add the method of dismantling and the working conditions of the building during the renovation.

A roof panel can shorten the closing stage of the extension. It does not, however, remove the problems of the old structure. First, the substrate, roof levels and water drainage path must be identified. The junction of the two parts requires particular attention. A well-prepared detail should account for their separate movement, not merely cover the visible gap. Check the condition of the wall or steel frame that the new roof slope is to approach. Determine whether loads can be transferred at that point. A cladding wall, a weak lintel and an old wall with voids are not equivalent supports. The assessment must be based on a structural survey.