The tax shall be calculated based on the floor area of plans submitted for a building permit. "Floor area" for purposes of this section shall be as defined in section 10-3-100 of this code. Where a field survey indicates that the floor area subject to the tax exceeds the floor area upon which the tax was calculated and paid, any additional taxes shall be due and payable prior to final city approval, or occupancy, whichever occurs first. (1962 Code § 8-9.05)