Need advise on room dimensions

I am setting up a 3 light set set up. From my research I found that a 4x8 room is the perfect size for 3 600 but my buddy at the store told me 8x12 . I was told my hoods have a 4x4 foot print. Now I am getting ready to start construction and I feel to be stuck on what's the best way to go. Any thoughts suggestions would be appreciated.

I made an error my guy at the store said 4x12 instead of a 4x8. Does it really matter? I far as i know yield is tied to your light not space.

If you do that u will need serious air flow and an AC unit.

You want to shoot for 50w per sq ft. rule of thumb. Your calc gives 56w per sq ft and your buddies 37w. Your buddies may yield more total weight, but yours would be higher quality, tighter, denser nuggets on average. Another thing to consider though, is that the 600w HPS is the most efficient of all in turning watts in to lumens, so you may be able to stretch that 50w per sq ft rule a bit south, you will also be getting overlap from each light, which helps, so it is more efficient than say if you had 3 600's in 3 seperate 4x4 tents/rooms. I'd say the guy at the store is probably closer to being right, but you may want to split the difference and go 4x10.

i agree with kt420. 4x10 would be great. i also agree with capt plant it, i would use 3 A/C reflectors (6 or 8 inch) linked together, sealed, pulling air in one end, expelling from the other. now if you're getting to make up a grow space, lol, spend a couple hundred more and get a light mover and move the =600w=600w=600w= setup side to side and build your room 8x10!!! (moving back and forth in the 8' direction). then you'd have the freedom to move around or set up a prepetual (spelling) flower room.