I'm guessing you could really make that as large as you want, eh? (sorry, I'm Canadian)
I've thought about how to construct a big ass smoker. The top voted recent restaurant here in Toronto is a smoke house called the Stockyards. He built his smoker 6 years ago, and it's basically 6' x 6' x 6'. Thick steel, she is. Other smoke houses here have had to order new smokers, as the production is just too small. Smoked meat has taken Toronto by storm.