I saw a similar design in a
magazine about chickens, they called it the "chook clock", and had it as a
tractor system for vegetable beds.
Chicken pie sounds better though : )
I guess how long the forage would last in your drawing would depend on the size of the yards. In a cold climate I would probably make the strawyard/dirt bit fairly big, so that they have somewhere comfortable to be when the forage needs to recover.
What are your ideas about how to do the gates? That has always seemed like the trickiest thing to work out with this kind of system.