a fabricating jig for building components is disclosed , including a horizontal frame , a pair of longitudinally extending stop plates connected with the frame for relative transverse parallel displacement toward and away from each other , and a device for displacing the stop plates together , whereby structural components arranged therebetween are pressed together and are held firmly in place during the fastening of the components to form a building unit . stud supports are connected with the frame between the plates for supporting structural components that extend transversely between longitudinal components which are in contiguous engagement with the stop plates , respectively . preferably the stud supports are longitudinally adjustable relative to the frame . an elevating device may be provided for raising the assembled building unit from the frame .