The biggest outlay of time and money when it comes to getting a backyard flock started is the chicken coop. And it's worth every minute of work and every penny of cost to make sure you've built a secure and safe home for your chickens. Small oversights now can mean loss of eggs or even your whole flock later due to environmental hazards or predators.
When it comes to construction, there are basically 2 kinds of chicken coops: portable ones, sometimes called chicken tractors and permanent ones. Whichever you choose, they can be as fancy or simple as you want.
The main difference between them is size, though there is no reason why you couldn't build a large portable tractor or a very small permanent pen. It depends on your situation, and how you want to raise your chickens. The simplest of the two is a permanent one, since you don't need to worry about size or navigability. Specific details that are unique to portable coops will be explained later.
Your first consideration is the location. Depending on your climate, you'll want your chicken house to be protected from strong winter winds and also sheltered from hot summer sun. Needless to say, this is not an issue with portable coops since you can put them wherever you want. A small city yard may not offer much difference from one side to the other, but a little thought at this point can save you some hassles later.
The size of your coop should be determined by the number of birds you plan on keeping. More or less, you want at least 4 square feet of space for every bird though allowing more room for them is better if you can manage it. Consider this the minimum. Once you've chosen a chicken breed, you'll be able to determine how many birds you need to keep for the egg or meat supply your family needs. So you shouldn't wait until the coop is done to think about birds.
Inside the Coop
The basic idea for a chicken house is really just a large box, so the exact design isn't all that important as long as it has a few certain features.
It will need a low doorway for the chickens to get in and out of, that can close securely at nights. So don't just cut a hole. You need to have a door on it. Besides the chickens, you need to get in and out as well. This can be achieved in a number of ways, so feel free to get creative. A tall coop with a person-sized door is the simplest idea, so that you can get inside for cleaning and egg-collecting.
But with a little ingenuity, a few well placed doors can give you reaching access to the inside for these chores without having to build the whole coop large enough to accommodate you. Just remember that you will need to reach pretty much everywhere inside to clean properly, not just the next boxes for eggs.
And speaking of nest boxes, you'll have to have those for your egg-laying chickens. If you're raising chickens for meat, they are not really necessary. But for laying hens, you need to have boxes roughly a foot square for your hens to lay in. They may not use them, so don't assume all your eggs will be so conveniently placed. Chicken's instincts make them more comfortable laying and sitting on eggs in a confined space, so you really need to provide boxes for happy chickens. You don't need to have one per chicken though. Have maybe 1 box for every 3 to 4 hens. Since you will be collecting eggs frequently, the boxes will be empty most of the time and will allow multiple hens to use them.
When not sitting around in the nest boxes, chickens will want a place to roost. They won't be happy having to stand or sit on the ground all the time so you must have a place for them to perch. A length of 1-inch wide dowel or railing across the coop should do fine. Your chickens will perch up there, and sleep there too. Position them so that it is very easy to clean underneath because most of the waste will build up there.
Your next consideration will be the roof. Whatever material you decide to cover the roof with, it must be waterproof. You shouldn't just use bare plywood, even if it seems adequate for security reasons. Water will seep through and a drippy coop will give you sick chickens in no time. Cover the roof with tar paper, asphalt sheeting, shingles, metal panels or whatever you have around that will prevent any moisture from getting inside. If you live in an area that gets significant snow fall each winter, you will need to build your coop with a slanted roof so that the snow can slide off.
And don't forget the floor. It may be tempting to simplify your building by leaving a natural dirt floor, but it's not a good idea. It's harder to clean and will allow predators or pests to dig up into your coop from below. The most secure would be a concrete pad, which may be beyond your do-it-yourself abilities. A wooden floor is a bit more typical though it can (and will) rot over time because it is in contact with the earth and it can be chewed through by determined rodents.
A common compromise is to build a raised wooden floor, using deck blocks or patio stones to create an airspace between the earth and your coop floor.
A few other things to consider for your coop building. Ventilation is very important, more so than most beginners realize. Add some vents towards the top of the coop at a minimum, and its even better if you have at least one window that can be opened. The inside of a chicken coop is a warm and very damp place. If you can't get fresh air in and moisture out, your will have sick chickens in no time. In both cases, you need to make sure any vent openings are secure with sturdy screens or hardware cloth to keep out pests.
One last feature for the inside of your chicken coop should be mentioned, and that is the lighting. If you live in an area with relatively mild winters with long days, you can probably get away with no lighting at all. But once the amount of daylight goes down in the winters, your chickens will inevitably stop laying. This can mean no eggs for several months. To keep them laying longer in the winter, add a few extra hours of light each day. Light bulbs can also provide a little extra heat.
In areas with cold winters, a light bulb is a valuable heat source as well as a source of light. Chickens can tolerate cold temperatures fine without extra heat, but a light bulb can make a world of difference. A red one can be left on all night without interfering with your birds' sleeping patterns. A well-insulated coop will hold in the heat, but any added insulation must be out of pecking reach of your chickens. That means you can't just line the inner walls with foam panels. Insulation must be sandwiched between solid wood walls.
That covers the building itself, but the bedding inside the coop deserves a few words as well. You need some kind of bedding material to absorb all the droppings, and to allow your chickens to scratch around as they constantly do by instinct. The best choices are wood chips or straw, though straw is definitely the cheapest unless you can get wood chips in bulk. Sawdust isn't a good material as it can make your coop very dusty, and the chickens are more likely to ingest a lot of it as they pick at bugs on the ground. You'll be changing the bedding regularly, so choose something that you have easy access to. The chapter on Cleaning and Care has more on bedding.
The last word about building a coop is that it must be tight and secure. There is a long list of possible predators for your poor chickens, so you must keep them safe. This goes double at nights, so all doors must close and latch shut and all open spaces must be blocked with heavy screen or wire.
The Outside Pen
While you can technically raise chickens strictly indoors, most people who run a backyard flock want to allow their chickens access to the outside and fresh air. If you have a secure and closed-in yard, you can free-range your chickens or basically just let them roam around without a pen.
At the minimum, you should have at least the same amount of space in the outdoor pen as you've provided for the inside space (based on the number of chickens). But the more space you provide, the happier your chickens will be.
Your outside pen serves 2 purposes: to keep the chickens in, and to keep predators out. If your overall yard is well-fenced, you won't need to build your chicken pen with a focus on predators because they are already kept out by the yard fencing. Then you can build a lighter pen with simple fence posts and chicken wire. It should be at least 4 feet high, though smaller bodied birds that are prone to flight may be able to hop that. In that case, go for a 5 to 6-foot fence.
When there is any chance of a larger predator getting at your chickens during the day, then a stronger pen is required. Sturdy woven-wire fencing and solid posts should stand up to most attacks. But remember that most predators do come out at night, so the pen only needs to protect against day-time threats. A top is a good idea if hawks are numerous in your area.
For added security, bury the bottom 6 inches to a foot of fencing underground to deter any animals from pushing under the fence. A very determined predator may still dig under, but most will give up after a few inches of digging.
Like the coop, you will need to have access to the pen area for cleaning and raking. So you should have a door that will let you in, not just a door from the coop for the chickens.
Small yards or small flocks would be the most suitable for a portable coop. The benefit from having a pen that is movable is that you can shift it around in your yard, giving the chickens access to fresh patches of grass for scratching and bug-hunting.
The standard design for a movable chicken tractor has a fenced-in pen attached to a small enclosure, with wheels under one end of the house portion. Add some handles to the other end, and you can move it around sort of like how you move a wheelbarrow. Pick up one end by the handles, and push.
Be realistic when building a portable coop, and test its "liftability" throughout the building process. It's very easy to overestimate how much you can lift, especially once the nesting boxes and roosts are added inside the coop. Many flock owners have gone this route, only to end up with a tractor they can't easily move more than a few inches.
If you are adding a fully fenced pen (including the top), you can build it fairly low to the ground because you won't need to get inside while it's in place since the whole things lifts up anyway.