Nothing in this Section shall be construed to prevent the collective provision of off- street parking facilities for two or more buildings or uses of similar character, provided the total of such collective off-street parking facilities shall not be less than the sum of the requirements of this Section. A written agreement between the parties shall be filed with the application for a zoning certificate, stating that the proposed joint parking area will be developed and maintained jointly and by mutual agreement. The location of such joint parking shall conform to the location requirements of this Section.