You could get a cheap 6X4 shed and adapt it and put a 6X6 run on the side. This would allow lots of room for 3 -6 hens.You would need some kind of substrate on the run floor and my own preference is gravel. The larger type is best. That way you can hose it down once a week and the dirt falls to the soil beneath and is eaten by worms.Ideally the run also needs to be covered. The run also needs to be wired under the gravel to prevent vermin digging in and the shed should be raised 6 inches to prevent hiding places for rats. This also means that you can pop a poison bait box under the shed to control any rats.
Depending on the breed of dog you have, you could easily train it to disregard the chickens. In my yard, I have my 3 plymouth rocks, plus 4 assorted large mongrel hens running loose. When I nbrought my new collie home I just let him loose. He ran over to investigate and I just stayed to watch. He simply sniffed them and then tried to herd them into a corner. I told him to leave them and now he acts as though they don't even exist. However, I would not trust a terrier of any kind with my birds.
I hope you do get some chickens as they are great pets and after some 30 years keeping fowl I STILL get a buzz when I find fresh warm eggs in the nest.
That said, oddly enough, I'm not keen on eggs and probably eat only 6 in a year. In the winter, my dogs, cats and ferrets get most of the eggs. In spring and summer I sell most for hatching or I hatch them myself.
