The new concrete segmented folded plate dome roof of the new auditorium at the University of IL in Urbana, is one of the largest in the world, although its appearance suggests delicacy, like fine fluted porcelain, rather than massiveness. In constructing the auditorium an excavation was first made for a circular foundation grade beam 48 inches deep with an outside diameter of 250 feet and an inside diameter of 218 feet. A steel tower 100 feet high was erected in the center for temporary support. The top of this tower served as a platform for casting a reinforced concrete ring. Forms for the dome extended from this ring to the perimeter of the building, with three intermediate supports. Concrete was placed for one 15 degree segment and then placed for the opposite 15 degree segment until the roof was completed. Vibration and finishing were carefully carried out to assure maximum density of concrete. Web thickness of the structural lightweight concrete is 3 1 /2 inches with valleys and ridges somewhat thicker.