Whenever a multiple dwelling shall be erected, there shall be provided upon the premises an accessory garage or garages for use only by the occupants of said multiple dwelling in a ratio of not less than 1 1/2 garage spaces for each dwelling unit. In lieu of such garage spaces, there may be provided upon the premises parking spaces providing accommodations for an equal number of automobiles. Said private accessory garage or garages or parking spaces shall be located at least 15 feet from the multiple dwelling building except where contained within or upon said multiple-dwelling building. However, where the area between the multiple-dwelling building and the accessory garage or garages or parking spaces shall be used for driveway purposes, then the garage or parking spaces shall be located at least 20 feet from the multiple-dwelling building. Each parking space, exclusive of access area, shall be not less than 8 1/2 feet in width by 20 feet in length and shall be graded, paved, marked and provided with adequate access consisting of travel lane or travel lanes having a minimum width of 20 feet each and dry wells for drainage purposes, all in accordance with requirements of the Incorporated Village of Hempstead. Parking upon the multiple-dwelling premises shall be restricted to those garage spaces or parking spaces specifically provided therefor by the owner.