The vertical distance of a building measured from the average established grade at the street line or from the average natural front yard ground level, whichever is higher, to (1) the highest point of the roof's surface if a flat surface, (2) to the deck line of mansard roofs, or (3) to the mean height level between eaves and edge for hip and gable roofs and, in any event, excluding chimneys, cooling towers, elevator bulkheads, penthouses, tanks, water towers, radio towers, ornamental cupolas, domes or spires, and parapet walls not exceeding ten (10) feet. If the street grade has not be [been] officially established, the average front yard grade shall be used for a base level.