Building coverage. The area occupied by buildings shall not exceed 15% of the gross lot area of each lot, and no more than 5,000 square feet for commercial uses, except that no more than 6,500 square feet for office uses shall be allowed. However, where the gross lot area is one acre or more, the maximum building coverage shall be 10% of the gross lot area of each lot, shall not exceed 10,000 square feet for office uses and 5,000 square feet for all other commercial uses.