I am a strong believer in reclaiming lumber and building materials.  I've got a lot left over from the wienie wagon reclaimed materials project, maybe enough to build a chicken coop.  Find me and I'll arrange for you to come over and look at it and (hopefully) haul some away.  As they use to say in the 70s ... "I took too much ma-an."

Otherwise (not sure if this is strictly legal or not) some people raid dumpsters at area construction sites.  Also, you can even just "ask" and they will occasionally give you stuff, they're throwing it away, after all. But that is up to you as my friend Chip Stewart often says, sometimes it's easier to ask for forgiveness rather than permission. There are a couple of particularly ripe looking ones on Lake Ave between first and second and a few down on Michigan st in A&L development zone.

The Common Ground Reuse Center, though a little tricky to find is the place to go. Take W. Michigan off of 40th Ave. W. and turn right just after AMPI. Their prices are pretty good and they've got a lot more than plywood. http://www.commongrnd.org

Common Ground closed last summer I believe. It is a shame.

Bummer @ Common Ground. I've got their fridge magnet up on the filing cab by my computer. There usually isn't much in the way of cheap plywood at Menard's, but they usually have a bunch of handyman-type boards available.

Demo Licious?

From what I observed in Tijuana; any respectable chicken coup needs to be framed around either an old washing machine, dryer or deadlined auto.  Kinda like Tom's Burned Down; but on a smaller scale.