Abstract: A system of mounting a plurality of wall panels to a soffit layout which defines the building module's layout, utilizes exterior and interior wall panels which are hingedly mounted at the bottom and are actively displaced to permit the casting to be removed. The panels are movable through the use of manual or hydraulic actuators. When the interior panels are positioned to receive the mold material they are exactly vertical. To permit the creation of orthogonal corners, the invention employs a trapezoidal corner panel for use in each interior corner. This corner panel is movable independently of the wall panels although it fits in precise confronting relation with specially designed terminal sections of the wall panels. A spacer or filler segment is also utilized above each interior wall panel and outwardly of the marginal roof panels with the filler segment defining a horizontal junction for the casting wall and roof.