I'd say it is. The barn I'm at has 12x12 stalls with an outdoor 12x12 paddock attached so they can go in and out when they want to and see other horses (24x12 altogether). Most barns just have a 12x12, which are fine as long as they get plenty of turn out. The smaller the stall, the more turn out they need.
Thanks everyone for your opinions and input.. I think I am going to go with 2 12X12 stalls. I have another building to keep hay and bedding in. I do want to have a small tack room. I also want to have small paddocks coming off each stall. We have 43 acres. We currently have 3 seperate pastures and each one has a small barn/loafing shed. I have had horses all my life and never had an actual barn with real horse stalls,, its about time. thanks again..