Building grow cab

if you have a good venting system then you dont have to worry about the heat or just use 400 hps lamp
keep up the good work

You are going to have a heat problem with that 600 watt hps unless you plan ahead and get some good ventilation going. If you haven't purchased your light yet you may want to look into an air cooled light. It will make a huge difference in your temps.

So far the plan is to have a small fan something like 65cfm to 95cfm on each side of the intake and exhaust system. the intake will be on the back high right corner and the exhaust will be on the side as well as a carbon filter with a vent out of the box. maybe I should add more powerfull fans?

I would make sure that your intake fan is near the bottom and the exhuast fan is near the top.

you also need to consider the height of the lights and your growing medium. When I built my first cabinet it was 48 in. and I was using it from seed to harvest. The problem was that after I added my reservoir and the space that my light needed I only had 24 in. for my plant.

I know that I will probably get slaughtered on this but have you considered using LED's? I use them and have had pretty good success, expensive though.

To use a 600w hps in that small a space it will definately need cooling imo. I have one in a 5'x5'x5' room and it takes a fair bit of cooling, before I built my cooltube I had temps as high as 105f! It takes a 240cfm fan just to cool the bulb! At the mo it's also exhausting air from the room as my intake temps are a few degrees above freezing, but when it gets warmer I'll be switching to seperate systems.
I would suggest something like a 100-150cfm fan just to cool the bulb, and a similar one to extract air from your room. You might get away with less if your ducting is short, and doesn't have any bends or restrictions like a carbon filter, but it's better to have too powerful a fan than not powerful enough, you can get controllers to turn it down but if it isn't big enough you can only get a better fan. Better ventilation than is necessary won't do any harm, but inadequate ventilation leading to high temps won't do your plants any favours.
Sorry if that was a bit long winded, I'm wrecked and can't figure out how to say what I'm thinking!

hey there jash...a 600watt whould be sick...it can work i got 2 400watters in a 2x2x4 cab, temps 75....but u need a cool tube with its own fan.. not sucking air from inside the box.. but rather from out side the box cooling the light then out...the box will need it's own ex fan..good luck and peace