Hm. That is an interesting question.
First, you have *probably* figured this out already but just in case - I'd be cautious having chickens in the tackroom, because they will make massive amounts of chicken dust all over your tack and brushes and blankies and all that. (Speaking as someone with an 'extra' saddle - for the totally retired TB - lives for mildew-avoidance reasons in the building with the chickens. Not the brightest thing to do
)
I would say that everything else being equal, open eaves would be better asa ventilation source than a single window. The eaves are presumably open on 2 sides of the building so you would get a crossflow of air, which is really what you want. All you have to do is hardwarecloth-screen them to keep predators out and make wooden flaps to close them off in case of storm, blizzard, excessive giant cold snap, etc. That is pretty easy to do. Ventilation into a horse stall is also a reasonable thing to do, particularly assuming the horse stall is itself somewhat ventilated (it sure oughta be).
OTOH, there is definite attraction to a rooof that is not just bare metal on the inside. Enough to outweigh the ventilation thing? I dunno. I'd guess not but then I am not *there*
And I am not entirely understanding where the tackroom is coming into play in all this. So, who knows. You decide
Pat, restraiing herself with difficulty from observing that you
clearly need more horses, heh heh heh (and don't start on *me*, I have an 8 stall barn and a very very large run-in, for just 3 horses, which is probably 3 more than we techncially need anyhow <g>)