A structure assembled from a combination of stackable modules, each module assembled from multiple prefabricated, transportable blocks. The blocks are typically reinforced cast concrete formed in reusable molds. Module framing blocks may include arched corner blocks, key blocks that interlock with a pair of corner blocks, and optional center blocks. Other structural elements include roof, floor, and wall components that interlock with the framing modules. Modules may be stacked or nested to form structures including buildings, elevated roadways, and parking garages. Utilities may be provided through optional conduits formed in the corner elements. The framing supports raised floor modules for ease in mechanical system installation and modification. The roof elements support usable terraces and rainwater collection. The blocks are demountable and reusable. The modules are self-supporting during erection, and may be assembled without fasteners.