I'm new here, so forgive me if this has been posted here before. It's a link to an article from the Virginia Cooperative Center on small-scale poultry housing. Lots of good information. Scroll down to the bottom to see the plan for an 8X8 coop.
http://pubs.ext.vt.edu/2902/2902-1092/2902-1092.pdf
http://pubs.ext.vt.edu/2902/2902-1092/2902-1092.pdf