When I first heard the term “chicken tractor,” I had to laugh at the visual. Even though I had kept chickens for a number of years and thought I had picked up the correct terms from hanging around the feed store while I got hay and chicken feed every few months, this phrase was new to me.
After a bit of research, I found that if I lived in England, I would call it a “chicken ark”: a cage for chickens that has no bottom (so the chickens are right on the ground) and it can usually be moved around from place to place in your yard.
The site on this link has lots of photos (no plans) for a variety of different styles of chicken tractors. My personal favorite from a humor point of view is about one-third down the page, and has a guy sitting cross legged inside the chicken tractor. You will notice that a lot of the tractors have built-in handles and wheels for easier moving around the yard. From a predator point of view, though, these tractors look like a racoon or skunk could dig right under them and get at your pet chickens.