I don't care if they have outside access to the paddocks, but after experiencing a barn fire, I would never build another barn that did not have outside doors in each stall.
My horses were outside when the fire started, but if they had been in their stalls, I would have had to enter the burning barn to get them out of the stalls.
Karen, I am SO sorry to hear about your barn fire. Thank god the horses were outside!
I was sleeping in the barn at a show a looong time ago and someone's box fan at the other end of the aisle started an electrical fire. That was one of the most terrifying experiences of my life! Luckily it landed on a rubber mat and did not spread, but the whole barn was filled with smoke. It was a scary couple of minutes while we investigated.
And no, there was no outside access to stalls.
Fire is the main reason I would prefer outside access to all stalls if possible. I'd love to have Dutch doors out the back of all stalls with windows in the top of the Dutch door. Plenty of light coming in, and I love the option to keep the top door open and let the ponies hang their heads out in the breeze. lol.
If you do add turnouts to your barn just make sure they are sizable. One stable I know of has very small turnouts just big enough for the horse to go out side (very small area). The stable charges extra for these stalls, and although it looks like a great idea or better choice these are the only horses that colic.