Abstract: A roof system is provided for buildings having an unventilated roofing support such as concrete forming a planar receiving surface. An intermediate plate formed of an environmental-tight sheet of plastic material is placed on the planar receiving surface. The sheet contains a uniform pattern of protuberances such as frusto-conical studs having planar tops. A rigid roof covering formed of corrosion-resistant metal plates such as zinc is laid on top of the planar surfaces of the studs. The plates have interfitting, bent edges forming troughs. The studs space the rigid roof covering from the intermediate sheet forming a ventilation space for collecting leaks or condensation.