A retirement community may include common areas and facilities wholly contained within and accessory to a multifamily structure, to be used solely by the residents and invited guests, and not by the general public, for a community room, fitness center, hair salon, gift shop, flower shop, dining hall, medical exam office, physical/occupational therapy office, multimedia room, administrative office, building maintenance, or uses of a similar nature as determined by Council. Common areas and facilities located within a multifamily building (i.e., not exterior common areas such as walking trails and gazebos) shall not exceed 15% of the total gross floor area of all of the multifamily buildings located in the retirement community.