I don't know what climate you live in or what type of goats you have (meat or dairy), but do you NEED a goat barn? I live in a very mild climate, rarely under 30F or over 85F. They live outdoors most of the time. I have places for them to get out of the rain that have dry bedding and keep their minerals dry. I keep Kikos.
If I were to build a goat barn, I'd leave it open and put up pens as needed.