Since the sheathing had to be replaced anyway, the author increased the roof slope by adding tapered 2-by sleepers on top of the joists.
The EPDM installation started with a 1/2-inch-thick fiberboard underlayment engineered to bond with the roofing adhesive. It scores and cuts like cement board and is fastened in place with galvanized screws and washers.
The membrane is left long, then folded up the wall and trimmed to its final length. To minimize cuts, the corners are folded over.