Sorry it took so long for me to get this posted!
Guess it depends on if you want things like breeding pens or if you're gonna just have a flock of laying hens. You're lucky you're starting out with an empty barn to beging with. That way you can figure out just what you want and design the best way to accomodate. Just remember to allow room for More chickens than you plan for. A couple things you might want to consider are a large storage room. Its amazing how it fills up. A brooder area for chicks and a grow out pen. A separate area for sick chickens or those in need of extra TLC. And a quiet corner for a broody hen if you want them to set.
Heres mine. Looking at it in pics it looks a little... shall we say rustic? Its a 16'x40'. I had to keep the box stalls in there for the horses when it gets real cold. Other than that they're in a separate in and out building. I tend to scavenge for my materials so things are kinda built according to what was on hand. You can see the little pop door for the box stall. Everyone in that pen gets to free range. Here goes:
Looking in the people door I have the main coop on the right and storage on the left
Left side of main coop:
Right side of main coop I have an upper deck brooder area:
Then past the main coop on the right I added a smaller coop and on the left is one of the box stalls that I converted to a pen. Everything in the box stall is removable so it can still function as a box stall in the coldest weather. The little box is for the cats so they can get in to eat but any chickens can't! And then there's my brooder which I can move into my entryway if I have chicks in winter.
Here's looking back towards the people door. Had to put a little door on hinges for this pop door cuz of the window and I really like it. I also have cheap sheeting that I can tack up on the screened areas when it gets real cold and I run a heat lamp:
Here's the outside pens. I set up a smaller run within the larger run for the smaller coop:
So thats what I got. Hope it gave you some ideas. Good luck with your project!