I good idea to use those enormous barn beams. I can't wait to knock down one the barns and put its bones to better use! Of course, the barn wood will be used to side the exterior of the potting shed, chicken coop, etc.
Millers outbuilding - A great selection of design ideas for potting sheds. Lots of inspiration here for the DIY enthusiast. The one pictured has at least 2 good ideas I like: a covered entry and a sliding barn-style door for equipment like a wheelbarrow or garden wagon.