Chicken coop building plans are a less expensive option for the person who is into DIY.
Apart from the great guides offered below, I also recommend that you check out Bill Keene's Building A Chicken Coop. It is extremely comprehensive and detailed but its step-by-step approach makes it very easy to understand. This guide offers plans for various sizes and styles of coops to house from 4 - 50 chickens. It includes portable units, single level, and double story premium coops.