An apparatus and method for forming hollow concrete structures or shells in which the top, bottom and sides are formed into an integral unitary structure by rotating an assembly of reinforcing members to enable the concrete forming the top, bottom and side to each be finished in a substantially horizontal position with a minimum of forms. Openings for doors and windows may be formed by using suitable blanks that are prepositioned prior to pouring the concrete. Also, suitable end closure members can also be formed in a flat or horizontal position inside the unitary structure for subsequent erection in a vertical position.