Abstract: A building module for use in construction of a building comprising a deck oriented in a horizontal plane and a plurality of hollow structural members extending downwardly from around a periphery of the deck. A method of constructing a building comprising placing a plurality of modules according to a floor plan to form a story of the building, pouring flowable medium that sets to a become a solid structural material into the hollow structural members of the plurality of modules to form structural columns, pouring flowable medium that sets to a become a solid structural material onto the decks of the plurality of modules for form structural slabs, and allowing the structural columns and structural slabs to set to complete the story of the building.