It will be inside my 40x50 structural steel shop with a thick slab. Just a plain flat roof is what I had in mind, but I do want high a ceiling............tall ceiling is not a problem in this shop. It will need to be strong to support anything want to hang from it.
Even though it will be sealed and running CO2, does fresh air need to be introduced from time to time? Is there any value to do it on some set cyclical basis, despite needing to add CO2. Winter time, this would just cost a little propane.
It will be an ongoing project, once the room is built, I'll move my current equipment over and what I have for a couple grows, except for the portable a/c. Automation will be a must and that will have to be the next step. After that will be the lights. I kinda think I'll be switching to HLG. With 6 grow areas, I'll need 5 lights. That's the biggest expense of this whole project.
Edit.....no building permit needed out in the country.