There are different weaves of fibreglass for different applications. Not sure what flat roofs use. Here we used fibreglass mat for fillings, and cloth for the bottom coat. You probably use fibreglass cloth. The epoxy resin is definitely similar. Possibly the same.
None of that fiberglass that is laid down over that gel coat is going to hold If you don't get it down to raw glass you're just going to get a delamination
