how old are you, and why do you need to build a box if you're growing in your closet anyway? Don't think you can hide a grow-op from nosey people that live in your house. As a matter of fact, it is nearly impossible to hide from people tht live in the same house as you. Only thing i can think of that would be a surefire way to hide it is the attic. Other than that, any grow box that will fit in your closet will do. Just make sure you got a propper exhaust, so that the hot air from the box doesn't end up accumulating in the closet but gets blown out the closet instead. Also, a cool air intake from outside the closet is needed as well i suppose.
Yeah, if your in a house with other people, they WILL find out eventually, if you plan on having a succesfull grow. This stuff STINKS if your growing it right, my entire apartment smelled like weed for 2 months or so when i grew my one plant. Otherwise, in my closet i didnt even build a box, i just had the plant in there, with one of those window fans exhanging air in and out. But seriously...this is a big and smelly operation if you want results.
You can all but elimate the smell if you are using an enclosed box with a nice, air scrubbing (carbon filter) setup. I made my own carbon filter for about $30 the Friday before last. It has been doing great! Here is the guide I used: http://www.gardenscure.com/420/security/60127-ryoko-builds-diy-activated-carbon-filter.html ...and pictures of mine: ... ... ... ... ... ... Check out the link in my signature for more pictures, etc.