longitudinal and lateral motions the crane 39 is employed principally for supplying heavy parts from the stores 36 and 37 to the sub line 16 and for moving the completed ceilings 83 from that sub line to the intermediate store 12 a further overhead crane 43 is movable longitudinally of the manufacturing line 10 on rails 42 and laterally of that line with the aid of a transverse gantry or crane crab 44 it will be noted that the rails 42 extend over the mounting depot or station 35 of the assembly line 7 so that the hoisting gear of the crane can be employed to deliver walls floors and ceilings from the intermediate stores 11 12 and 30 direct to the mounting depot or station 35 said walls floors and ceilings 80 to 83 are assembled at the mounting depot or station 35 to form the building sections or room units the same crane 43 may be employed to move skips or other containers of liquid concrete from the mixer 17 to the various molds on the three sub lines 13 14 and 15 the crane 43 and its rails 42 afford conveying means whose path of possible movement crosses that defined by the four rails 9 it is advantageous to provide ducts beneath the sub lines 13 14.