For any building or portion of a building developed or enlarged after February 3, 1977, a minimum of 20 percent of the lot area of the zoning lot shall be provided as usable landscaped open recreation space accessible to the occupants of such development or enlargement. Such open recreation space may be accessible to the public.

Such open recreation space shall be located at the ground level and/or the roof level. However, if such open recreation space is located both at the ground level and at the roof level, not less than 40 percent may be located at either location. Such open recreation space shall be landscaped and properly maintained in accordance with the provisions of Section 109-142.