Will you partition the space for veg and flower? Will you have a clone room? Will you have a double door so you can enter in the day time without exterior light polluting your grow? Do you have a large budget? How many Amps do you have available on your panel? Thats a big limiting factor for bigger indoor grows.
Depending on your desire to pay for electricity, LED is the best way to go for numerous reasons. However, the upfront costs are steep. You would reduce heat load a ton and in the long run electricity usage would ve way less. WARNING!!! Do NOT buy blurple lights! Have a look at HLG lights before you buy anything.
Or if you’re interested in DIY, you can pick those boards separately and wire them yourself.
Another option is COB lighting. Rapid led dot com has 4x4 fixtures that you wire together. I have a 4x4 fixture from them and it grows great from seed to harvest. Definitely don’t buy a blurple fixture.
Otherwise you’re looking at CMH, MH, HPS for lighting if you don’t want the upfront costs for LED.
yeah @Covertgrower has that right about the cob style and HIDs, just keep in mind some lights are more power hungry, inefficient, than others and your power panel will tell you if you are overloading your circuits!
Remember you will need to be able to run HVAC and lighting and pumps or whatever you need, at the same time! You dont want to swamp your wiring or your breakers, ideally you want some headroom there.
that is so, hid does create heat for sure! So maybe price out some 600w MH for veg and some 1000w HPS for flower? In general, the veg room can be smaller than the flower room.
Most larger grows have 3 rooms, a small clone/ prep room… place to store fert and mix. A veg room and a flower room. With this setup, you can perpetually grow crop after crop. The other option, is 2 separate veg/ flower rooms, the only thing you change is the bulbs, the plants never move. You have room vegging and the other flowering all the time.
Keep in mind, you also need a place to dry and trim thats a lot of weed!
This is an ambitious project; I’m going to throw out there that it might save you time/money/frustration/legal issues to dial the scale back to something like a 4’x4’ partition or tent. The consequences of failure seem heightened with this kind of square footage.
That covers you legally, but I’m talking about the expense. If it’s something you can grow into, you’ll probably make fewer missteps.
I’d start with a really thorough assessment of the outbuilding, and come up with a priorities list of improvements. If you have access to a thermal camera, they’re really useful. If you can add even more insulation, all the better. If there are opportunities for pests to get in, they’re probably going to.
The lighting isn’t that hard to solve for, and it’s pretty much about throwing money at the problem. I’ve found that it’s the other stuff that has me chasing my tail.