A system for the formation of a sloped roof surface on a pre-existing flat roof deck through the utilization of a mold assembly comprising a plurality of angularly configured beams spaced from one another and cooperatively interconnected with baffle plates and an overlying grill structure having a substantially open or pass-through construction to the extent that a confined space defined by the above set forth component is to be filled with a light-weight cementitious or other operable material preferably suitable for roofing, resulting in an inclined or sloped outer surface being formed contiguous with the grill structure such that the cured cementitious material and aforementioned components become a substantially integral, one-piece construction permanently secured to the pre-existing, original flat roof deck.