We use a dog kennel as an extension of our run so the chickens can be locked up while we're on vacation. I agree with everyone else's comments and I'm sure you already have lots of help... but I just wanted to add a few things.
If you're considering adding a roof, you may want to use a tarp. We recently added a tarp to the top of our kennel and it keeps the hawks, rain and snow out quite well (chickens are NOT snow fans...

)
And for the ground: On the ground of the kennel it might get muddy on wet days (which can spawn parasites if there's open water) and your chickens might get bored if they're kept in the kennel for a long time. Though it is not necessary, both of these problems can be solved with a layer of pine needles or temporary straw on the ground.
Anyway that's it!