It really depends how "contained" you want your grow operation to be. A 600 watt will put out 90,000 lumens, divide that by 5000 lumens/sq ft and you get 18 square feet. That's a little bit over a 4x4 foot area. Efficiency is your next question. If you have more reflective material surrounding your plants, less light is lost and you can grow more plants or the plants you do have will grow all that much better. A more contained grow area would most likely mean more reflection if you painted the walls white or something to that extent.

Also, a contained environment has the benefits of better smell containment because without a decently small volume such as an enclosed grow box, it becomes increasingly hard to filter all of the air out of an area through a carbon filter. Remember that the volume is the CUBE of the dimensions. So going from a 4x4x4 container/cabinet to a 14x14x8 room means a lot of extra air to take care of and "clean"

These are just some ideas you should start thinking about. Good luck!