A link to a page or an explanation of the rationale / differences of all methods of commercial roofing would be great. Built roofs, modified bitumen, single-ply, etc. Thanks. What I discovered was – For a gable roof (for example, most of the houses) – which would consist of burlap ceiling connected to the joist then roofing lath nailed on top (the distance depends, apart what tiles / slate you are using). Then you would end up applying the tiles, song, etc. For flat roofs (eg garage roofs) – which would consist of plywood nailed to their existing beams if in good enough condition, then the layer of roofing felt 125 stuck on top using bitumen then another layer of felt on this occasion 250 roofing felt, then the roofer would use green mineral to make their flash-ens, which is the border of the roof, which turns the perhymeter then most would applying a reflective finish paint. And most of the stores that you see will be in a form called coating im not connoisseurs like you never done it myself, I hope this helps a little. .