Floor area ratio shall be calculated by dividing the total floor area of all buildings, as measured to the dimensions of the outside walls, and enclosed accessory structures (whether designed for occupancy or not) in square feet, on a lot, by the total lot area in square feet. Total floor area shall not include: (1) cellar or attic as defined in the Uniform Construction Code of the State of New Jersey; (2) multi-level parking structures permitted as a conditional use in the OR District, and (3) porch, deck, terrace balcony or similar provided same is not enclosed by walls, windows or other construction and does not have a roof.