Abstract: An improved roof and floor deck system uses conventional steel shapes and sizes to form a preassembled panel that can be installed and fastened in place without the need for welding or other fastening from above. The roof and floor panel assembly has a frame of generally C-shaped structural members, including a pair of side members and a pair of end members. Each member has a substantially planar outer perimeter surface for coupling with an adjacent panel frame member. A deck is secured to enclose the top side of the frame. The panels are prefabricated, hoisted into place on existing supporting girders, connected together and secured to the girders by workers positioned below the panel assembly.