I just started one today!
Honestly, I went to Menards looking for ideas lol I just got some 2x2's, chicken wire (I have some screen laying around that I can put around the bottom), and a piece of 2'x4' plywood. I'm sure it would have been cheaper to use a 4'x8' piece and cut it, but I only have a hand saw, and I really didn't want to do that
I cut 6 pieces at 4', and 8 pieces at 21" (So they fit between the 4' sections, and the plywood will still cover the bottom). I made a frame with those, and then my drill died
I Will be attaching the chicken wire on the outside of the frame, then the plywood on the bottom. I got some vinyl flooring for free, and that will cover the bottom, and a few inches up the sides. I also framed in the top, so I can put hinges on it. I didn't explain that very well. I will take pics when I am done! Have fun, and happy building!
Oh, I have also read that you can use a plastic bin or cardboard box, with some sort of screen on top, or an aguarium. It just depends on how many chicks you are planning to get.
ETA, mine cost about $25.