I am getting ready to start building a large outdoor pen for my new pekin ducks. I currently have it all planned out but keep adjusting the size a bit. I keep going back and forth between the size of the enclosed portion and the size of the run. But once I figure that out, what type of wood is OK to use for the main structure? I was going to use pressure treated lumber but then got to thinking if that was safe for them with the chemicals used to treat it. It will be a 2x4 frame with plywood covered in siding for the enclosed part, then 2x4 frame covered in welded wire mesh for the open air run. They are still only a week or so old, so the pen would be outside for a while airing out before they go in there. I could use any type of wood that's best. My budget is about $300 or so, and the way I've priced it with the pressure treated wood, it was under $200 with the welded wire. I can get siding scraps for free and I have some shingles left for the roof. Thanks for any info and tips.