In about an hour I was able to construct a "nursery" for a hen and chicks. Make a rectangle out of boards (I did 4 feet long and 2 feet deep). Run board vertically from each corner (I did 3 feet high), then make another rectangle at the top. You now have a rectangular prism. Close in the sides with either plywood or hardware cloth. Framing out a little door is very easy to do. This thing is solid, predator proof, and even rat proof. The main con is it's a huge pain to clean, but good for a temporary solution.
Were I to build it again, I'd put one whole wall of plywood on a hinge for easy opening.