Regardless, you would still need a barn about 30ft X50 ft in length. With that many birds, you will also need a place to store your tools, equipment, and have adequate grain storage. I have a horse barn, and I use 3 large drum barrels to store grain- I'm thinking you would need more than that with 300 birds. Even with my horses and 3 large oil drums I still have to go buy grain every two weeks. It can totally be done! And you can have 300 birds quite easily, but you do need a large enough barn to do it. I would have the barn plumbed for water and wired for electricity. Otherwise, watering that many birds could be a real project if you don't think hard about how to incorporate those things first. I would recommend a nipple system in that case, too. And if you're going to do that, then you'll need to heat your barn (just a little) to keep your water from freezing (if you do get freezing temps). Also, think about using Roll Out nest boxes. With that many birds, they will likely eat the eggs or break them. They make industrial metal roll out boxes or you could always make them yourself. You may want to think about having a built in brooder area into your barn that would be heated or support the wiring for heat lamps.
BTW- even if you don't get cold- you will still need the barn for night time predator protection and for a place for your birds to roost.