I'am preparing to build my first smokehouse. I want it to be 4'w x 4'L x 8'H with a one foot roof slope. I was going to build it out of sheets of plywood with a tin roof. Question, What do i need to use for the inside walls that wont contaminate my food? Tin, Wood etc. Also i was wondering if it would be a good idea to insulate the walls to hold in the heat. Thank you for your help.