Well, you can make it as small as you want. Mine is 3' x 5'. Large enough for a nest box, a little roost, food and water, plus some space for moving about.
"How to Build a Hoop Coop" on YouTube.com. the poster is Square County Homestead
I built one. You need a drill. I covered mine in chicken wire, then a tarp. Then, take rope and latch it on the big pvc pipe, throw it over the top and tie it to the other side. You'd need 3 or 4 of those...