Mine was in the house, and was part of the utility room with space stolen from and over large bathroom. It had long saddle racks around two walls and lots of hanging space for bridles, coats etc, with storage boxes underneath. The was leather never mouldy, and I could clean in the kitchen or outside on the patio if the weather was nice.
One yard I used to do a bit of work at had a big but not huge tack room, indoor as the yard was all under one roof but it had a proper height ceiling so storage on top!
It was painted, had a little kitchen area, only tiny but a few units, sink with hot and cold water, fridge and kettle.
A sofa with blankets on and I think proper heating, it was always lovely and warm, which also of course kept the tack in good condition.
There were shelves with boxes for boots/ extra bits of everything.
It was a lovely place to hide away in terrible weather