I have chickens in the city, so my coops are pretty scaled down. The larger one houses 3 chickens and I like it cause it's something I can walk into. The tractor is new we just got it off of craigslist last week and it houses 2 young Bantie EE's. Pro's about the tractor is it can be moved around the yard. Tractor is 4X8, the larger coop/run is 5X8 about 7 ft tall. Both coop's were made by other's my husband is not real patient or skilled so I leave things like this to someone else.
Our chicken coop is a series of buildings, all connected, that were already on the property when we bought it. We just cleaned them up and prepped them to be "chicken proof" from hazards, and viola - Chicken coop! Plus, we turned some shelves into nesting boxes, and put in some logged young trees as perches. All in all, it is three connected buildings (one for sleeping, one for egg laying, and one for the roosters) that are each about 11x16'
I would never buy a chicken coop from someone, as it wouldn't be big enough, and would be far too expensive if it were. Plus, most chicken coops come with tiny runs - We like to supply our girls and boys with lots of acreage!