I'm sure a lot people already do this, however some might not. Tell people you're building a coop!! I work at a school and I told a couple of the ladies I work with I was building my coop in a month or so. One ladies husband works at a prefab home building place and gets free scrap materials, as much as he wants. After talking to the guy, my coops going to be around even if there's a nuclear attack!!! He said he has 25 to 30 sheets of 3/4" pressure treated plywood in his barn that I can HAVE!!!! Most of the sheets only have a corner or something small like that cut out of them. He said he's seen siding, double pane windows, misc lumber, etc, etc in the scrap pile for free!!! Tell people youre building a coop and ask around. You never know what somebody else has for "junk."