Here ar esome pics of the build of the smoker and grill I built this year. I wanted the firebox to be offset to better control the temps. The ceilings and floors of the smoker and firebox are a mix of refractory cement, perlite, and lime. I couldn't find a local welder that would give me anything resembling an affordable price to custom fabricate doors. I ended up ordering a 2'x2' and 3'x3' fire rated doors that were meant for fire extinguishers in walls that I painted with high heat grill paint. I installed the vents and cut the openings in them with a jigsaw (went thru a few blades!). I purchased the handles separately and had them welded to the knobs that came with the door. I ended up needing to add insulating tape to inside of the doors to get them close to air tight. I should have ordered a slightly larger charcoal basket, but once up to temp, it maintains a constant 225-250 temp for close to 3 hours with little or no adjustment. VERY happy with the end result!
I have architectural plans I could share, but I can't figure out how to attach a PDF file.