A one-family dwelling, which may include the office of a physician, lawyer, licensed architect, licensed engineer, surgeon, dentist, real estate broker, artist or musician, when situated in the same building used by such physician, lawyer, surgeon, dentist, real estate broker, artist or musician as his or her private dwelling, and which may also include customary home occupations, such as dressmaking and millinery, conducted by resident occupants thereof; provided, however, that any such office or occupation shall not be conducted in a basement or cellar, and shall not occupy more than 1/3 (33 1/3%) of the gross floor area of said dwelling.