Planning commissions, building codes, and frequently common sense can dictate to the owner of a new building that he needs a square foot of parking for each square foot of building. When the parking lot next door is going to cost $1.50 per square foot, as it often does in choice locations, the owner is better off on a first cost basis to use rooftop parking. Concrete is the best material for him to use, and when he does, the yardage on the job just about doubles. Not all buildings are suitable for prestressed concrete lift slab roofs, but when one is, the average $2.00 per square foot roof cost is the best buy an owner can make. The requirements are an uninterrupted slab at grade, reasonable column spacing, and a minimum of interior walls. Most lift slabs in California are prestressed for deflection and crack control, long spans, and favorable cost. The lift slab sequence is the same for either reinforced or prestressed slabs. Slab lifting is done for the same reasons that make tiltup walls economical. The slab is cast on the grade slab and jacked up to final position by hydraulic gear mounted on top of the columns. Lift slab and tiltup work will together; however the tiltup walls are usually cast on a waste slab outside the building line and walked to their position. The usual parking deck is about 15,000 square feet over an automobile agency, retail store, or office and light manufacturing buildings.