8ft x 8ft Grow Room Help

8x8 is a really nice sized grow room. IMHO 1000w hid hps won't quite cover 8x8 for flowering. You say you want to use all usable space, but it is nice to have a little room to walk around in and tend to the plants. So with a little walk way around the edge you are looking at 6x6, And either a 600w mh/hps or 1000w mh/hps would be a place to start. A place to START! not to buy. start means reading and asking around, which is what you are doing, so you are off to a good start
 
if it was me, I would go with one 1000w mh/hps. I use to grow 9 to 16 plants in 3 gallon bags under one 1000w. But life was not very efficient back then
 
oh yeah, if you are starting from seeds, consider feminized seeds, because one male messes up your grow space (in that you now have empty space)
 
and if you have a garage, if there is any way you could use some of that space for seedlings or clones or for vegging or sexing out that would put you way ahead

 

in that area I would  have 4x 600w HPS lights. The number of plants depend on the size of them. You could have 4 big plants under each light. Each plant taking up a 2x2' area. So that would make 16 plants altogether under the 4 lights. 
 
I'd have air cooled hoods for each light, and a 6" exhaust fan cooling each pair. Air coming in from outside straight through the hoods and straight back out. I'd then have an 8" fan exhausting the room through a carbon filter high up, and a 6" fan bringing air in to the room low down.
 
I'd have a recirculating hydro set up because watering all the soil pots on different days would be a nightmare

 

yes, the light is more intense in the middle, don't want to waste any space there
 
yield? I'll leave that to the experts. Too many ways to talk about it. Yield per plant? Yield per year? Yield per sq foot? Yield per kilowatt?

 

Around 8-12oz per 600w HPS light if all goes well 
About 14-18oz per 1000w light. But there are a lot of factors that effect this 

 

that would certainly be a top of the line set up
 
I like it all except the hydro
 
for us soil growers, watering is not a nightmare, it is a joy

 

 
I grow soil and hydro. A few soil pots is fine, but you have to water them on the day that they require it. Different plants will run the pots dry at different rates so if you had 16 pots to water, you will have to test them all every day and water some every day. Total nightmare when you compare it to hydro where you just fill a tank from a hose whenever you have the time once a week or so.

 

 
The initial cost of a hydro set up of that size is going to cost a couple of hundred I guess. But it's a lot less work and would be totally worth it imo.
 
A 1000w light max's out at about 5' in both directions so two wouldnt cover your area completely, but it would mean you would get some room in there for a small cloning tent

 

 
I edited my estimate, a 1k light can give you that much if you know what you are doing but it's probably a bit high for the average

 

 
how are you at building things? Drilling holes, cutting pipe, and stuff like that? Building an RDWC doesn't cost much. Buying a ready made hydro system can be a few hundred

 

 
It's what I would do, but I already know how to grow. A big set up like that is probably not best to start off with, I was probably wrong to suggest it. 
 
Your idea of 2x 1k lights would be simpler to set up and maintain. Less plants too so if you preferred soil it wouldn't so much of a pain to water.
 
I got too carried away with what I would do and forgot what would be best for a beginner starting out 

 

no, we should have it so bad that we have to use less artificial light. More is always better, but there comes a point of diminishing returns.
 
so your 8x8 probabably has 6x6 usable. You'd have to ask around, "What is the best light to cover 6x6 in an 8x8 grow room.?"
 
My answer would be one 1000w. But these hobbies tend to grow, and later on you will find those 600w a little more versatile, especially if you start fooling around in your garage.