Thanks to all for the replies. I tend to be obsessive once I start a project-- since 11:30 last night I've come up with a sketch for a mobile coop & run (tractor). I'll only keep 4-5 hens, since about 18 eggs a week is my target. (I'm estimating 5 eggs per hen a week.)
This sketch is shown with a 2' clearance under. From what everyone has said, I could get by with 18-24". There won't be litter under the coop, since it will be moved around. I may keep it at 24", since I don't want it to be too low to reach in when I need to.
Also, it will be completely roofed, for weather and sun protection (as well as Avian Flu). It gets HOT in north Texas! This would have 16 sf coop, with 44 sf yard. I might make it longer, but that could become unwieldy. Three 12" x 15" nest boxes will hang on the back (bottom hinges for those, so no leaky roof). Lots more design to go through though. I still have a few days... since I'm not starting the eggs until the Saturday before Easter. That means I have 9-10 weeks to get this done.
I'll post progress on this over on the chicken tractors forum.
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