Do the reverse flow smoker . I built my own reverse flow as you can see below in pictures . My tank is 250 gallon propane tank . I see in your drawing you have your smoke stack all the way down to the first rack level . I did the same thing when I built mine . I had issues with top rack being 70 degrees hotter than bottom rack. The issue was the heat was being trapped since heat rises . I had to cut my stack off inside the smoker and then that fixed the problem . Now I get 15 degrees difference between the racks . Make sure your intake, exhaust stack and opening from firebox to smoker is proper size .If to small you will have drafting isssues . I used the pit calculator you can find on line . Good luck on new build . Post pics as it progresses .