I have 5 chicken tractors that I move biweekly. Most of my chickens free range during the day and return to their tractors at night for feeding. I have nest boxes in 3 of the tractors and I will be building boxes for the other 2 very soon. As you can see, most of mine are open air type because we live in central Mississippi. We only have a handful of cold days, so heat is a bigger concern.
These were my first 2 tractors based on designs I had seen on BYC and some other sites. Most of the designs I saw used wood for the runs, but I was trying to lighten the load, so I used PVC. This is just 10' pieces of 1/2 inch PVC bent and pushed into holes drilled in the 2x6's. I am only 5' tall, so bending over to go in the runs isn't a problem. Each coop has nesting boxes on one side and a ladder type roost on the other. I put side doors, so I could collect eggs, but found these to be useless because I always use the big door in the back of the coop. The bottoms of the coops have 1/4 inch hardware cloth because that is all we had on hand at the time. 1/2 inch would have been much better, as all the poop would have fallen through. I put the red feeder trays under the roosts and that catches most of the poop and I can just dump them out periodically. A friend who has poultry houses gave me the feeder trays because he didn't like using them. They also work great to soak trays of seedlings in. The base of the tractors are 6x12 and the coop is 2x6. One houses a Buff Orpington rooster and 4 girls and the other houses a BO/EE rooster mix with his 6 BO girls. Each tractor cost about $100.
Below is my 3rd tractor. It was originally built to hold guineas, but they are all gone now. So it is the banty(my husband won't let me say bantam since we live in the south) tractor for now. As soon as I get rid of 2 BCM roosters, I will most likely move my 1 BCM rooster and his 2 girls to this coop. It is 4x8 and is now attached to 2x4's on the bottom to make it easier to slide and add weight. I was having to stake it down, because winds would send it tumbling. There is a roost towards the back and a milk crate that is serving as a roost for a silkie. It currently houses 1 Millie Fleur D'Uccle rooster and his 2 girls, a BB red hen and 1 silkie hen.
Below is my 4th tractor. I saw a similar picture on the web from somewhere in Guam. There weren't any plans, so I came up with some dimensions I liked (4x10 and 5' tall on the door side). This coop cost about $50. I used old tin roofing from a neighbor (free) and plastic bamboo outdoor blinds to create shade and a coop area. I cut the blinds up and zip tied them to the wire. I added so double bubble foil on the end for the winter. The nesting boxes will sit on the area where you see the 2 horizontal pvc pipes. I am able to move this coop and the 3rd coop around by hand.
My 5th tractor had humble beginnings as a dog pen. I borrowed it from a neighbor, to house my ducks in last year, and finally ended up buying it from them for $25. In order to make it inhabitable for chickens, we added a roof made of 2x2's and more free tin roofing. After enclosing with chicken wire, I zip tied double bubble foil to make the coop area. We added roosts and some nesting boxes. Oh, we strapped it to 2x6's so it could be pulled around by the 4 wheeler like the first 2 tractors. This coop houses one EE rooster and his seven gals.