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.