I turned a carport into a barn - probably similar to building it for a coop - just add in different interiors.
Edited by Mojo Chick'n - 2/4/09 at 10:16am
We got the carport - then put 2x4 along the inside wall, to reinforce those (we were using it for donkeys and horses - they like to rub and lean on anything that doesn't fall over ) For chickens you probably wouldn't have to reinforce the inside walls. We then put in a back wall (on one end) and an open front wall (on the other end) and built a stall in it about 1/4 of the way from the back wall. There are two windows in the back wall, and the front is an open large door.
The stall was to put hay into, and our feeder bins, to keep the donkeys and horses out of the feed, but it could be used for a pen for giving birth, or whatever. We are actually moving the feed and planning to put a door into the back of it, (off the pig pen we built) and use the stall as a "pig house".
A couple of things to make sure you do --
situate it so the breeze can blow through the ends of it, because that is the easiest place to put your windows and vents when you build the ends onto it. It gets hot in the summer (well, ours is green, a white one probably would reflect heat better, but the green absorbs more winter sun, if you live in a colder climate). Otherwise, you'll have to cut holes in the actual metal sides, which is easy enough to do, but they will have to be trimmed out with wood or something, because that metal is sharp.
Maybe put a blower vent in the top of it - one of those twirly round vents that just move in the breeze and suck the hot air out of the top - I picked one up at a yard sale for 15 bucks - not sure how much they cost new. I don't have ours installed yet.
Ok, I don't have good pics of the interior, but here is our barn....
eta - the ends were done with 2x4 framing and those wavy steel sheets - we bought a pile of them, used, for a buck each. We then painted it to match the rest of the metal, and the framing was white so we did the front and back framing in white, also.