We currently have an extension project on the go. Our builders have used our 7 year old existing flat roof essentially as a scaffold to access works. When it was installed we had skylights fitted and had some leaks around them. They were patched and no problems since. We had been told not to walk on the roof when it was installed and advised them of this. We also advised them of the patching at first installation caused by the skylight fitting. They told us it was fine and did it anyway. We’ve also repeatedly asked them to take care as they often have more than one of them up there at a time and the banging and vibrations have been bad. The plaster board in the ceiling is coming away inside and caulking splitting. We then sprung a leak in the ceiling away from the edge where the extension is being built. I climbed the scaffold and found the roof peppered with nails and broken slates... which they have been walking on. We have photos. They are arguing the membrane was of “poor quality” (argument doesn’t really stand as we warned them not to walk on it and it was dry before they did). My question is, what can we reasonably expect as a repair? My feeling is a patching job will not leave us with as robust a roof as we started with, and who knows if nail holes we haven’t yet found? I’m thinking they should cover the costs of replacing the full membrane to a standard of the membrane that was there previously? Thanks for any advice!