We actually done quite a bit of checking out on coops/runs before we made our purchase. We knew what features we were looking for, and how much space we had available, as well as how many chickens we wanted to keep. Initially we were quite taken by the coops of a similar style to ours that were/are being sold on ebay. We even saw several of them at poultry centres/breeders etc, with up to as many as eight full size chickens in them. However, we read several items on them being made of cheap inferior quality wood that fell apart in no time. Bearing in mind that those coops were actually only the smaller ones, with only two panels in the run part (as on ebay). We chose to go for less birds and more room, as our run has three sections/panels, plus the bit with lower headroom below the actual coop. When visiting breeders/suppliers, we made sure to tell them our set up, and all of them said it was plenty big enough for four chickens of the size we were looking for, and some said it could take more. It's actually advertised for up to five (the guy who makes them breeds chickens himself and is very knowledgeable, not just a get rich quick guy knocking them up in his garage), and we have seen the smaller ones advertised for up to eight in some places!! We knew that four chickens was all we wanted, so even though it could hold more, we don't want to do that. They all seem happy enough as they are. Eventually, once our garden is finished, then we hope to be able to place the whole thing inside another fenced off fox proof area, although we were told by most of the breeders/suppliers that they would be fine living in the coop/run just as it is. We have also seen several other people who have similar (and in most cases smaller) coops/runs with between 3 - 6 birds in them, and not all 'new to chicken keeping' as you might expect.
If I have one regret, it's that the whole thing is not standing up height, as hubby does have to get in on his hands and knees, but if/when we move them, I may open up the whole front of the run and build onto it, adding height as well as length/width, to make cleaning easier. It will be easy enough to do just by removing the big front double panel.
Unfortunately not all of us have fields with acres of land in which to keep our chickens. I only wish we did. Farming and Chicken Keeping have been in our family for generations. I remember my Nan keeping them in the tiny back yard of her house in London.