that's gonna be a massive barn to hold every passive mob with a loot table. Keep in mind that slimes are not passive so that doesn't seem like a plausible addition to the Ark
I would like to make a suggestion of a building that would be related to the pvp world/arena levels. How about Colosseum style/dojo style building with the ability to accept/submit challenges from/to other towns. I remember seeing similar scenarios in shows and movies, where a master or teacher was challenged for that schools sign. If defeated the challengers had the right to take the sign as a trophy and proof of the victory.
I'd say extend the roof all the way so that our lovely animals don't get wet when there's inclement weather. Also, for the chest into which all the drops go. I'd say see about trying to make it on the first floor. I can see it getting perhaps a little tiring having to climb the ladder every time in order to get to the barn loots.
I'm also hesitant when I see cobwebs and redstone torches, simply because on many texture packs (including default), they make the barn look dark, and a little gloomy. Though I can perhaps appreciate the homage to Charlotte's Web, perhaps just one spider web instead of more.
That's all of my critiques; otherwise, looks great!
I like it, unlimited. It's an effective use of space. I think the only couple of critiques ar that the placement of the chest is a little underwhelming (could look cooler or be placed elsewhere maybe) and that the roof should be spruce wood (if it isn't). Other than that, +1!