Wow, that's huge! Great, your chickens will love it. When I build mine, it'll be only 18 SF, 6x6x3 with a two-foot run underneath, very portable for moving around my yard as necessary. Mine will be only a tad generous for 4 birds, yours much more so.
I too am concerned about ventilation vs. drafts. Where oh where to place my vents to provide circulation but not ruffle feathers. Grrr.
Thanks for sharing. Can't wait until the next installment.