My coop is pretty much built. It just needs a door and to be covered with chicken wire, which will also be buried around the perimeter. I'm trying to keep it simple and safe so, for instance, I decided to have interior-only access to nest boxes, since I'll be going inside daily to check on food...
After reading this whole thread I was poking around at the local farm and ranch store and found this product for $6. Ingredients: zeolite.
I chuckled to myself, walked 15 feet and picked up a 40lb bag of Sweet PDZ for $20.