A storm water area charge will be imposed on a parcel at the time of subdivision or construction of a structure 121 or more square feet in area. The charge shall be based upon the gross area of the parcel less the area to be dedicated to the city for ponding, parks and wetland, and right-of-way for state highways, county roads and local arterial roadways, or pre-existing right-of-way, intended to be maintained as right-of-way by the city in the future. The parcel will be given a credit for any onsite storm water improvement, which has been oversized to serve other property. The charge for lots oversized due to individual septic systems and water systems will be reduced to the charge that would be imposed on a one-half acre lot. An additional charge will then be imposed if the lot is further subdivided less a credit for the charge previously paid. The charge shall be paid in cash before the subdivision is approved by the city or the building permit issued unless the city and subdivider agree that the charge may be assessed against the property. Property shall be exempt from the storm water area charge imposed by this section if the charges were paid or assessed in conjunction with a previous subdivision of the property or building permit and if the property is not being zoned to a classification with a higher charge.