Chicken tractor height?

[3chicksmomma]

I am trying to design our chicken tractor/coop, and am wondering how tall the space for their run under the hen house should be. They will have a 4x5 hen house, and directly under it will be their access to the run which will also go out 6 feet to the side. I'm trying to keep the whole thing from being to tall. I ordered 5 large sized birds (Buff Orpington, Black Australorpe, Partridge Rock, and two Wyandottes) and want to make sure they will have plenty of headroom. I was thinking about 2 feet at the max.

 

[The Chickeneer]

2 feet is perfectly fine for a small run. I have a run for the chicks and ducklings, it's 2.5 feet and thats plenty of headroom.