My only problems were when I made the chicken tractor too big or put
too many in a smaller one. My chicken tractors were built to be moved
by hand and were as Gene mentioned a low box frame affair.
Some chicken tractors are pretty big and pretty elaborate, more like
moveable chicken houses. If I were to make another I might try one
framed of steel. An old trailer frame might be faster and less
expensive than one built from scratch out of angle iron. I would make
it braced strong enough that it could be moved with a riding mower,
tractor or pickup truck.
One of the challenges here in the Ozarks is that the land is rarely
flat. So no matter where it is placed, the bottom of the pen usually
has gaps where a snake, weasel or mink would have no trouble sliding
in for a meal.
Coons here are the biggest challenge. I once killed a coon that was
trying to pull a pullet through the wire. More hassle, but a
double-walled design might stop them from reaching in and grabbing a
frenzied bird.