A composite building system includes a special joist having a lower flange in one embodiment and a special ladder reinforcement in another embodiment, a plurality of special masonry blocks defining a longitudinal trough, the blocks having mutually co-planar upper surfaces and at least one stepped upper edge, the stepped upper edges of the plurality of blocks running substantially transverse the trough in a grid-like pattern, a network of wire lateral reinforcement disposed in at least some of the stepped edges; and a flowable or fluid grout filling the stepped edges and the trough and, when cured, binding the joist or ladder reinforcement and the plurality of blocks to form an integral steel reinforced concrete structure having a substantially planar surface.