I've been running one for years in a similar setup in my shop. If you are reading this and have the capacity to construct such a unit I would. It is the greatest luxury to come back from a hard hunt and just string up the game in the cooler, come back to it as suits you, and with better results (just don't forget to extract tenderloins first). Mine gets lots of use and is busy through the entire hunting season.
I just used an insulated (cheap ext grade fiberglass door) and put in a window for it. Mine is part of other rooms in a mezzanine. I set up a small hoist that reaches down through the ceiling, through a little trap-door, and helps to lift critters and quarters into place--it is really convenient and I would recommend doing that. I have the smallest a/c unit I could find and it still over-cools and has trouble regulating temps well until you have enough meat in there so I wouldn't over-think insulation other than for efficiency, though there are some potential moisture issues to be concerned with. I was able to plan for mine and installed a floor drain which I also like. I also ran my wiring for the cool-bot through the wall and mounted it on the ext of the cooler which really beats having to get in there to check temps and make any changes, especially when it starts getting crowded in there! That required getting mini-jack extensions. I used runs of uni-strut on the ceiling with some L brackets that are really sturdy.