The dominant form of development in the planned regional shopping center shall be an enclosed commercial mall with a minimum gross leasable area of 300,000 square feet, which includes department stores. The mall shall be covered with a roof and have an interior courtyard onto which all retail establishments in the mall shall have their main point of egress and ingress. The mall structure must be centrally located upon the site of the planned regional shopping center. As used herein, "gross leasable area" is defined as the total floor area designed for tenant occupancy and exclusive use, including basements, mezzanines and the upper floors, if any, expressed in square feet measured from the center lines of joint partitions and exteriors of outside walls. This definition is limited to the mall and does not include separate freestanding buildings or additional stores as may be approved for the shopping center.