No advertising structure shall have a facing that exceeds 672 square feet, but it shall allow extensions of up to two feet on the sides and 5.5 feet on the top, excluding base or apron supports and other structural members. This paragraph shall apply to each facing placed on an outdoor advertising structure. The advertising structure shall be measured by the smallest square, rectangle, triangle, circle, or combination thereof, which will encompass the entire advertisement and is made based on the height and the length but not the depth of the advertising copy.