This is how my GH looked the first year i grew in it.
This is what it looked like at the beginning of last year.
I took an old metal shed i wasn't using removed the roof and put corrugated plastic on it. I put the white plastic on the lower sides so nosey family couldn't see in. I have an intake and exhaust fan in the gable ends ( I built sealed boxes around them so they would run more efficient). I put white panda plastic on the walls to add some reflection. I used CO2 the first year with great results last year i didn't run it and was really disappointed so this year I'm going to use it again.