24 feet clear to underside of roof structure is more than adequate to accommodate new auditoriums with stadium seating and for locating the projection booth above the promenade. This clearance also provides you with the opportunity to locate other elements such as toilet rooms, party rooms, offices, storage, etc., underneath the stadium seating. Factors to consider are how large you want the big houses to be (of course existing column spacing will impact this decision) and riser heights at the front and rear sections of the auditoriums.