This might be an interesting thread for you.
Factoring in the cost of materials (PVC, joints, Mylar, plastic tarp, PVC glue, etc.), it's probably better to purchase a pre-made grow tent that suits your needs. Buy once, cry once....
It appears my 3x3x3 is too small of a recommendation for this crowd.. If you're looking to go big indoors, then here's what I did:
I should mention, the larger the space.. the more difficult it is to control the environment.
except the smaller the space, the faster it heats up and cools down.... less buffer space. much easier to hold temps to gradual changes in larger areas
I guess I mean to build something that looks like mass' set up, just smaller scale.
Dislaimer: personal experiences may vary.
Update: Turns out building this in my garage is a lot better than in my room, so that's where it's gonna happen. I'll have about the size of a 2001 Volvo (currently occupying space) plus a little extra.