Michelleml, you have a great start there - I would have loved to have something like that on our property when we bought it. My coop is 10x14 so almost the same size. I put a dividing wall in it to make a coop of 10x10 and a feed room that is 4x10. I can't tell you how much I love that feed room. Being able to have all of my feed and supplies in one place and located conveniently to the coop is such a blessing - I used to have supplies stashed all over the place, wherever I could fit them in. My dividing wall has a door so I can go from the coop to the feed room and back without having to go outside. The bottom half of the wall is solid and the top half is chicken wire. I have had 50 birds in the coop and they didn't seem crowded. Of course during the day there aren't ever many in there as they are out in the chicken yard, so it is only at night they are all in there.
Checoukan - that barn is going to be so great - can't wait to see more progress pics.
Trish, for the inside walls on my coop, I used OSB that was $6.50 a sheet. I couldn't find it anywhere in the store and finally had to ask an associate and he showed me where they keep it in a stack out the front of the store. If I am understanding what you want to use it for, that would also work for you and is even half what you had priced out, and a quarter of what your DH paid!