Concrete is no problem for short periods such as in entry ways, aisle, etc. Main thing to be concerned about is that its not slippery . In a stall, ok with the stall mats as others have said. My concerned with livestock barns is head room. Most milk cow barns I've been in have a low ceiling. Unless the horse is very small or very very very low key, there probably isn't enough head room. You need much more than just so he can stand. Horses have a tendency to raise their heads when startled, etc and of couse they may rear up on occasions [img]/forums/images/icons/shocked.gif[/img] .
On finding and purchasing. be careful! Try to get to know the horse people in the area. Find someone good to help you, and never finalize the deal until you've had a vet check the horse.
A good dicussion board for horses is "horsecity.com".
Other than that, good luck. There's nothing better than having a good horse (well, almost nothing [img]/forums/images/icons/blush.gif[/img] )
Larry