I'd start with this one, and scale it down as needed to half, 2/3, or 3/4 size.

Here is a link that might be useful: Jake's chair

Norm Abram (PBS's The New Yankee Workshop) has done several Adirondack chairs. You can order plans from him and scale accordingly. I also think one appeared his "outdoor projects" book. Just make photocopies at your local library.

Here's a plan for $10: http://www.woodcraftplans.com/cw006.htm

Here is a link that might be useful: easy woodworking