I'm saying about 3 to 3.5 feet so you don't burn the colas on the top. I did that the first time because I was trying to grow a crazy sativa.And max you will probably grow 1 to 1.5 pounds. However if you put clones in there you can harvest pretty much every 2 weeks. The conclusion is if you build a room you will obviously get more weight but the box is ridiculously stealthy and so easy to move. I've grown in multiple spots in my house because of company and it keeps trucking. No one has any idea what it is. If you live in an apartment or townhouse GET ONE no questions asked. However if you have a huge basement or live in a house you might benefit from building a room. Its just a lot more work and maintenance. I hope that helps you and if you have any questions please feel free to message me again. I will be on more often from now on