Mini-greenhouse for winter chicken run?

[Poppy Putentake]

I've been thinking of either building or buying a mini-greenhouse to serve as a daytime winter run for a small (3-6) flock of hens. In the summer they free-range; I'm thinking they would benefit in winter from a place where they'd be sheltered from the wind and would have access to snow-free ground to scratch in. (Then in the spring, I could use it to grow vegetables protected from the chickens. ;^) )
I was thinking of something with a footprint around 6' x 10'. I think I could build something that size fairly quickly. Most of what I've seen available online is smaller than that.
I'm thinking this could also be called a "day tractor".
Has anyone else tried this or built something like this?

 

[SandyRiverChick]

I do open my green house in winter for the girls. They love it for dry dirt dust bathing and hanging out, like you said, sheltered from weather. It's absolutely to hot and off limits to them in Summer however.....