I wanted a chicken tractor that would be easy to move, hold 6 chickens happily, and not cost a mint.
I found some 20" x 10" tires on craigslist - big turf tires with a large surface area so it wouldn't sink into the wet ground that is Oregon's curse about 13 months a year (I'm rounding up a bit on the months).
I then had to figure out how to get them to work super easily, without making me grunt when moving the thing.
Hmmmm . . . it had to be all-but-balanced on those tires when in the 'ready to move' position.
Aha! Use a lever that I could step on. Stepping is the easiest motion to add force (my dead weight), and it allows travel over a reasonably long distance (I can step up onto a 30" tall desk with no big problem).
So, I have roughly 70 pounds (less than half my body weight so I don't fall over jumping up and down on the lever end) and it can travel roughly 24" (to leave room for the thickness of the lever, etc.)
I ended up with a bout a 5:1 ratio, so I could easily lift up a 350 pound coop, and more if I put more weight on my foot, and even more if I was willing to lift a bit on the handle of the coop when moving it.
It took me a while in my CAD system to convince myself it would really work the way I wanted, and when I built it - IT WORKED AS ADVERTISED!
It moves quite easily - even on wet ground.
The chickens are happy, I am happy, my wife is happy, the eggs are happy, the trees and the grass are happy, the clouds are happy!
Happy, happy, happy!