First Grow Box

Hey people,
I'll soon begin construction of my first grow box, very excited! I've got a tonne of guides and have pretty much decided to make my own from hardboard and 2 x 4, computers fans, the usual newbie set-up. Anyway, was hoping for some tips and advice, the loft I'll be growing in has about 6' clearance, maybe a tad more on the incline. What are the best dimensions for my grow box that would allow me to grow 2 or 3 plants to a decent size, with enough space for the light. I was thinking of forking out the cash for a nice HPS light that I could use for veggie and bloom cycle, but then again, I don't know what I'm talking about!
Anyway, looking forwards to hearing back from you all!
Happy toking!

Depending on the strain but all you would have o do is flower early.i start flowering at around 1 ft they normaly get up to around 4/5 ft when finished.but you can start flowering at 1ft and tie the heads down or i have been super cropping it is great if the plants getting a little tall it's a little scary if you havent done it b4 but it is easy bro just pince the plant where you want it too fold over squezze realy hard and roll in your fingers not to hard with the rolling bit and the plant will just fold over i leave it a day or two then i put some gardening twine around the fold.the plant will do a kind of u shape grow and start growing up the side of where it grew b4.you can do this with more than one brance any that are too big and the good thing is they all think that they are tops so you end up with some big nugs.go to see more buds on you tube not sure whitch one its in dvd1/2/3 but if you see it done it may be better then my explanation or just put supercropping into the you tube site. Good look dude keep them lights has close has possible then you may not have to do any of this you want nice close internodes.