Biggie is right on on all his points.
When I and 2 buddies built my trophy room - outside walls 12X6 pine log, interior walls and ceiling finished in 1X12 ship lap siding - I had some extra logs so we made the sidewalls around 9 ft - this is as much height as you need for deer - and even at that deer hanging anything over about 5-6 feet is too high unless you have lots of space. Bigger mounts can hang as high as 9 ft or so OK, otherwise you'll end up looking up the nostrils. Moose are ugly enough without looking up the nose. Ditto on the double doors. The room is 20X22 and I wish it was bigger. - search "trophy room" in the subject and my handle in the member name and you'll see some pics. --- I like the log and wood siding too because you don't need to worry about hanging on studs at all on the exterior, and even the interior walls are plenty to support deer mounts just in the ship lap. Any type building finished on the inside with this type lumber has a nice "cabin" feel.
Ryan