I usually start my new chicks in the brooding house we built from an old bunk bed. Maybe I'll post pictures of that some day even though it's not made from pallets. Then the chickens are free-ranged after the first 4-6 weeks. I tried free-ranging my meat birds two summers ago, but that didn't turn out so well. The Cornish meat varieties are bred to put on weight quickly. They say they go from birth to freezer in 8 weeks. Mine have always taken more like 10-12 weeks though because I let them range instead of packing them full of corn. This makes for a healthier bird on my table. Even my free-ranged meat birds grow too fast for their legs though. This makes them extremely susceptible to predators. Laying hens run pretty fast. Meat birds do not.
I needed a way to protect my meat chickens while still getting the benefits of a free-range diet. I've seen plans for several different chicken tractors online, but all of those involved buying additional materials that I didn't have readily on hand. I decided to rig something out of the lumber and chicken wire sitting around my house and yard, and of course I used some of the pallets.
In this picture I used another pallet for the lid. I meant to build a nice hinged lid, but I actually never got around to doing that. Maybe that will be a project for next spring.