A method and apparatus for manufacturing reinforced wall panels and reinforced roof panels and using the pre-manufactured reinforced wall and roof panels in the construction of a building structure at a building site. The reinforced wall and roof panels are molded using a molding medium consisting of two part polyurethane which is mixed with Portland cement. Reinforcing members and exterior weather resistant materials are placed within a mold and the mold is filled with the molding medium by injection or by pouring. The filled mold is then placed within a press to ensure against expansion by internal pressure caused by curing of the molding medium, thus ensuring dimensional accuracy of the finished panel. After hardening of the molding medium, the mold is removed from the press, opened and the finished panel is removed from the mold and is stored until the molding medium has completely cured. The reinforcing members and weather resistant material constitute integral components of the building panel structure.