I can't do it anywhere else mate, the attic is my only choice. I've got 24ft in length & 8.5ft in width with 6ft at the highest point going down to 3 feet. I've never done this before so I'm starting with a tent. After a few grows & as my experience increases I may extend further into the attic area.
Where are you venting to mate?
I understand mate! I wonder how other people fit these tiny tents in every day living! Hence mines small tent. Just to though floor boards and in the ceiling of what ever room (make it go to a corner) just put vent cover on. Won't even notice it. Just need stronger fan as Pushing down.
Then do your best to frame your grow room walls and ceiling at least 6 inches thick so you can insulate it well(R-19). Do your best to isolate the grow area from the extreme cold and hot enviromental swings an attic can have.....