a deck assembly\u0027s durability is greatly affected by the waterproofi ng membrane\u0027s selection and then overall. enclosed pergola | patio roof designs | porch blueprints. after. layout your rafters. all photos courtesy halsall associates. you\u0027re considering a new flat roof, it\u0027s wise to know the challenges inherent in this type of roofing it comes with far more challenges than sloped roofs, . loft conversion flat roof dormer in build #3.