Hi Alwayswantchics,
This dog house will convert nicely for a few chickens. I would find some rounded branches that have the bark removed. We found some nice slightly curvy branches that were floating in a local stream and brought them home. You can also buy some two by two's (which are less expensive than two by fours, and cut them to fit in side the dog house. Just nail either of them inside the across the dog house. The front opening and the bottom can be wired. It's best to use hardware cloth, which is just wire that has very tiny holes. I believe it comes in half inch, one inch, etc. The smaller the hole the better. You can tack the wire on with fence staples. The front can either be tacked to a one by one frame that you can attach to one side in order to open and close, Add a latch lock for security. If you hens will free range during the day that is all you need. Otherwise, you will need to build a wire run. There are lots of ideas on BYC as to how to construct one. If you were to attached a closed in run, you could either raise the dog house off the ground with some four by four posts and build the run out of one by ones or two by twos for the frame.
Have fun building!