As far as carpentry goes, building a box is the equivalent of vincent vangou doodling a pair of tits on the back of his homework.
As a stealth cab grower, I'd say your most important issues will be heat build up, and not enough headroom for flowering- you always see an awesome stealth grow all set up on here, with all the lights on over some seedlings, but then you notice the lights are already up as far as they'll go- now what the fuck? You think they'll grow like pancakes??
venting your box is simple even for ppl who cant afford a real inline fan. I have a 6" round flexible vent running up to the bottom of my box with a 15$ fan that fit the hole blowing in fresh air, then at the roof of the box there is another hole, with another cheap fan blowing the hot air out. I had 2 150 watt hps in there and temps in the 90's STILL with all that air!! I did get 2 harvest like that, but in this summer heat I'm switching to cfl because they dont heat up a box as bad
so just remember, FRESH AIR, HEAT, HEADROOM- or FAHH as we all call it on roll it up
peace