I found some large windows for cheap and took them to a glass shop and had them cut to my size. I then cut some frames and installed the glass. 5 windows cost me 23 dollars with the glass cutting.
Hey I'm with you. This summer I found two pallets for heavy machinery 4' x 6' x 10' for the bases. I also have a local newspaper company which puts ads out begging for you to take the pallets behind the building. The good wood is saved, the bad wood goes in the fire pit.
Just remember that many of your predators are also protected by game laws and such. Particularly the Owls. Just be careful when you make the decision and only point the gun at something you're willing to kill. Once the bullet leaves, it can never be taken back.
I'd include a sketch of what you want to do. Then everyone can get a better feel of what to use. If you use 2x6 or 2x8 you may be able to stretch the 4x4 vertical distance.