The most important thing is the safety and relative comfort of the occupants. It's a dangerous world if you are a chicken. Since I was using a 6 x12 dog run as my enclosure I had heavy pipe and chain link that I knew no predator could bend to gain access. However, any determined raccoon, fox, dog or cat could dig under the pipe, so I lined the floor of the run with hardware cloth and since chain link is large enough for a paw to slip through I also lined the inside perimeter with chicken wire. Chicken wire is quite flimsy and I would never use it alone since a determined predator could tear it apart. Hardware cloth, which is really wire, is much stronger. I also buried a 12" strip of chicken wire on the outside of the run as a deterrent. All the wire is connected to the bottom pipe. My chickens are as safe as kittens as long as they are inside their run. I designed their coop using three sheets of plywood and some 2x4s. I had some leftover metal roofing material that I used as well. The dimensions of the coop itself are 3x6, it is basically a box on stilts, with a bunch of hinged doors for access. Inside there is a 2x4 perch that spans the six foot length. This is where the chickens sleep. Chicken feet are not designed to grip, so using the 4" side of a 2x4 for them to perch on is more comfortable for their feet. Instead of putting a solid floor in my coop I wired the bottom with hardware cloth and then cut two pieces of plywood to fit on top to catch the poo. Fact: Chickens poop a lot at night. I made a hinged trap door that is the full length of the coop that I use to clean out the poop. I just partially pull out the plywood pieces and scrape the poop onto a bin. Easy. Above the trap door is the nesting box also with a trap door to gather eggs. I can do all this without ever entering the run. Above the nesting box is a window for ventilation. Inside the run on the other side of the coop is the small door and ramp for the chickens to enter. I recommend painting the interior so you can hose it down once and a while. The raw wood will absorb the poop and odors. Make no mistake, keeping chickens is messy enough, think about ease of cleaning before you commit to a design.
You may have noticed, there's a lot of talk about poop. That's the bad and the ugly truth! I'm a neat, dare I say, freak. Keeping the chicken run and coop clean is a chore. I read somewhere that keeping chickens was as easy as keeping a cat. I believed it, until I had chickens. So before you design your coop or shop for one, keep the above in mind. When doing my research I used Pinterest and Google, as well as backyardchickens.com. There are endless examples of chicken coop designs and ready made coops available at every price point. I encourage you to do as much research as possible before you step into the chicken keeping world. Most of the information out there has a rosy tint, very little bad or ugly. But you should know the all of it. As always, I welcome any questions you might have.