My best suggestion is to read the article posted here about building coops. There is one that is rather lengthy and has LOTS of pictures, from the ground up. It's extremely elborate and probably more expensive than my house, lol. But don't let that discourage you! Read it and learn! Use what you can and drool over the rest. I can't really describe what you need in proper detail, but yes, I wish I had dug down around the perimeter of the building and poured a concrete footer. At the very LEAST I should have put cinder blocks at the corners on sand, leveled, for support - BUT, snakes and/or skunks could have gotten under that where there were gaps. And it's so rainy and soupy here it probably wouldn't have helped much. Let me see if I can find a link to that article. I don't navigate here very well. Anyone wanting to help me out is welcome to do so.
Edited typo.