Abstract: A roof system and method of roof fabrication for a building having in place a plurality of parallel and spaced apart elongated structural support units defining a longitudinal surface exposed from above. Fabrication is effected by first applying a double faced adhesive tape longitudinally along the top surface of the support units after which flexible moisture impervious sheeting suitable to function as a vapor barrier is sequentially applied in lengths from rolls in a laterally spaced apart relation directly onto the adhesive tape of adjacent support units. This is followed by applying another length of sheeting intermediate and in contact with double faced adhesive tape applied over the borders of the adjacent previously applied sheeting into an overlapping seamed relation to render the sheeting continuous and uninterrupted.