Most tractor coops plans that I have looked at were rated at no more than 8 chickens. We ended up getting 14 chickens and I needed a tractor coop big enough to house them and light enough that it could be moved around. I had seen a photo of a coop that looked sort of like a stage coach with a screened run below it. The finished product that I ended up with is seen in the photo.
The coop is 8 ft long, 4 ft wide, and 4 ft high (plus the roof). The nest box attachment add about 2 feet on one end and has three nest compartments. The watering system consists of a kitty litter bucket on the roof that feeds water via vinyl tubing to a PVC pipe that has four chicken nipples installed in it. The main floor of the coop consists of half inch hardware cloth that lets the dropping fall through to the ground below. There is a removable ladder through an opening of the hardware cloth that lets the chicken go down to the ground below to eat grass and bugs. The whole structure rests on four 10-inch wheels. In the main compartment there are four 4 ft perches mounted laterally across the side walls. There is a drop-down door on the back of the nest boxes for access to the eggs.
The coop is comfortably large enough for the 14 chickens. I was worried about them not having enough roosting space with the 16 feet of perch but it's actually too much. One time I had seen 12 birds perched on one four foot bar. I also knew that the 32 square foot of screened ground below the coop is not nearly enough space for the chickens to roam around it. My plan was to release them regularly from the coop to roam where they want. The entire coop is surrounded by a 165 ft portable electric netting fence that is energized by a solar charger. The purpose of the electric fence is to keep predators out and not keep the chickens in.