A three bay concrete hangar being constructed for the British Air Ministry utilizes a roof erection method which is new to Britain and which has been employed only once anywhere in the world. The method involved casting on the ground a 180 foot long by 120 foot wide prestressed concrete barrel vault roof for each bay and jacking the resulting 1400 ton sections to an ultimate height of 46 feet by means of four 200 ton capacity hydraulic jacks at each corner. Simultaneous with the construction of the roofs, 1,000 T-shaped sections, each weighing one-half ton, were cast on the site for the columns.