Base kit SSM300 builds two half-relief or one complete industrial unit/warehouse. The walls are solid plastic with groves on the inside face to show where to cut in order to fit the various windows and doors. Multiple kits can be combined, including the SSM315 extension pack to double the half-relief depth, to create buildings of any size. Extra doors and windows (SSM314) and extra roller shutter doors (SSM313) are also available to completely customize your building.