You are very welcome to take a stroll through my website and click on "diary of a barn" and see mine in progress. Our new barn was well thought out and planned right down to the dollar. But there are still things that I wish were different, but I am not complaining.
I can tell you that bigger is better. Whatever size you think you need, make it bigger. You will find that you never have enough storage space or stalls.
You will also find that no matter how much money you plan to spend, count on it costing you double that.
When Geese said "condensation" that really struck a nerve:
it should be insulated to moderate temperatures and prevent condinsation
My old pole barn was built "on a wing and a prayer" and we just used whatever we could afford at the time, which wasn't much.: plywood, 2 X 4's and 4 X 4 posts and a tin roof. But that darn tin roof I swear. When snow would melt, it would literally "rain" inside the stalls getting the horses and bedding wet. It's been horrible and nerve racking.
Right now, steel and concrete seem to be holding their prices while wood continues to sky rocket.
Be aware that if you buy anything pre-fab that the price will be way high due to the built in price of insullation. So you may want to see what you can do on your own. If you can swing a hammer without busting your thumbs, you may be in luck. Go online and you will find some plans to look at.
Do a google search and put in words such as "barn buildings, horse habitats, metal barns" etc and see what is out there for ideas.