Hey bobank thanks for the response! I am fairly nee to it as well but you will find, if you haven't already that the folks on here are extremely helpful and have a lot of great ideas.
To answer your questions, what are you referencing when you say 40"x40"? The smokehouse stands about 7.5 feet tall (with concrete foundation. I do have a natural vent at the peak of the roof that runs all the way down but I also intend to install a 3 or 4" vent in the roof. For heat I am using a 3 propane burner from Northern Tools I just purchased (the link was posted by the legendary DaveOmak in this thread) and for smoke I just bought an
AMNPS that I will have mounted in a mailbox to the left of the smokehouse and piped in through a 3" aluminum dryer vent through the bottom. Also as far as the door goes I built it out of 5/16" Tongue and Groove paneling so when it does expand it will have some room to wiggle. I am also installing some stove gasket all the way around for the door to butt up against. When building the door I placed 1/4" shims around it until I installed the hinges so that once the door was solid there is 1/4" all the way around of free space to alleviate expansion. I even thought about spraying the door with oven paint to deflect some of the heat away from it. Again even after a year on this site and I am still learning new things.
Stay Smokey my friends.