I built my coop 3 years ago this summer. It is 8x7, dirt floored and lots of hardware cloth for ventilation. At first, I only had 2 hens, then the following spring, 6 chicks were added. The first 2 hens scratched the dirt continously and kept the earth/poop well turned. No mess, no smell. After adding 6 more, there still was enough dirt that there was no smell or mess. We had the hottest driest summer in 60 years with temps over 100 degrees for 2 months straight. I guess the poop never had a chance to smell, it was dried and dessicated immediately. I even watered them a coople of holes every evening so they would have cool earth for the next day to wallow in. Still no smell. Thanks to vanilla scented auto Christmas tree air fresheners, no flies either. Throughout this entire time, I have thrown vegetable waste in the coop, kitchen trimmings and scraps, grass, leaves, and spent plants from the garden.
Last November, the coop finally got a little smell to it. My neighbor started cleaning his garage and had sacks of sawdust from his table saw. I cured the coop smell with the sawdust. http://www.backyardchickens.com/t/608219/how-to-scare-the-be-jesus-out-of-your-chickens
I added sawdust several more times through the winter. Each time, the girls churned it into the dirt and as the sawdust disappeared, so did the poop and smell. It started getting kinda deep in there, the feeder hanging from the rafter got a lot of dirt kicked into it, the cinder block I had the waterer sitting on was half way buried. Yeah, time to clean it out.........so today I did. I dug it down a foot or so and was rewarded with 9 dump wagon loads of black crumbly rich compost.
this is the link to the dump wagon I used. 600 pound capacity.......HAH!! I feel like I have pulled about 100,000 pounds today
As I dug down, yes it was smelly, yes it was damp. So I threw some scratch in the coop so the girls could dig around and help dry it up in there. I will let it air out for several days or however long it takes, then I'll put sand in the coop and go back to sawdust and start the process over.
All this being said, my hens have never been dirty or smelly. They have been healthy, happy, spoiled to their treats, and have given us lots of eggs. They have not been tons of work, they take little time to care for daily and the rewards are great. We enjoy our chickens and consider them out pets.
My plan for this month is to add onto the coop and make a run for the girls, so I can get a couple more Chicken math..................