The gross unobstructed surface area, in square feet, of a permitted accessory group parking facility including stalls, aisles, driveways and maneuvering areas shall not exceed 200 times the number of accessory off-street parking spaces provided. This size limitation shall not be applicable to off-street parking spaces permitted under the provisions of paragraph (c) of Section 16-12 (Permitted Parking for Non-residential Uses) where such spaces are exclusively accessory, no-charge, self-parking spaces in enclosed facilities with a capacity limited to 100 automobiles. In such facilities, the gross unobstructed surface area, in square feet, shall not exceed 300 times the number of accessory off-street parking spaces provided.