Most zoning bylaws in major urban areas specify parking spaces based on seating capacity for cinemas, not based on sqaure feet, as in retail space. These standards generally range from one parking space for 3 seats up to one car for seven seats. This ratio depends on wheter the site is close to mass transit, whwther it is in the core of a city where other parking may be available, or if it is in a suburban area and depends on car access. So, for 600 seats, you could require anywhere from 85 cars up to 200 cars. Figure that you average 100 cars per acre (43,560 square feet) will allow you to calculate roughly the area you would need for parking.