Use OSB instead and paint it with oil base paint... I have built my coop out of it and have no problems with it. The sheets I used were about $6.00 each (I figured if I get 4 years or so out of it I can re sheet it if need be). Leave particle board alone----your kitchen sink and counter tops are usually made from this but have formica covering them, and if they get wet it is ruined. Plywood just costs too much, If I'm building a house maybe I'd use it,,,but for a coop?? I won't (of course I've built things all my life ( helped with several houses/ shops/ barns)- it pays to have the tools at your disposal.
If you build it ((think))- your sheets are 4ft by 8ft, built it to the dimensions so that you don't have to cut as much...I have a 10 by 10 and had to cut several sheets. If you use metal for a roof- build it to 3ft widths (the sheet is 3 ft wide) it is a pain to cut metal if you don't have the tools.
Just my 2cents- hope it was helpful.