The construction of buildings can be time consuming and error prone. Building modules constructed off-site and pre-furnished can be made more efficiently than building everything on-site. Building modules are disclosed with a reinforced, precast concrete floor with thickened edges, and a structural frame that defines the shape of the module. The frame is made from hollow structural section bars that are attached to the thickened edges of the floor. The module is made with a roof to protect the furnishings and fittings inside the module during storage, transportation and installation.