When installing a flat roof, we top the frame of the roof with plywood sheathing and an underlayment. Then, we bevel the corners, dry-fit the roofing, and glue down the roofing material. Finally, we finish the edges. How long the project takes depends on the size of the roof. Our flat roof installation in Cincinnati, OH has to put up with a lot of abuse from harsh weather, so we choose materials well suited for it.