Your extraction fan is going scrub a certain amount of air per hour. Your smells will fill whatever space you have. The smaller the space the easier it will be to control and keep clean. Absolutely nothing wrong with using a big room but my guess would be you are going to spend more money and more effort trying to control your environment than you would if you just bought a tent.
whatever you decide before your plants get into flower run your extraction and smoke a nice big fatty in the room. If you can smell it out I side or if someone comes in the room 10 minutes after you are done and it still smells thenyou will have issues.
A 4by4by6’ tent will have 100 cubic feet of air. Your room will have 1300 cubic feet, and probably not as sealed as you think. To scrub that much air will not only require bigger more expensive equipment but you’ll be scubbing a lot of air that you don’t really need to.
Now if your going to run 40 plants at 4 square feet of floor space per plant then you’ve got the perfect room and get some really big equipment and let’s get this party started.