I keep everything super clean and DRY. The only time there is a smell is if things get really wet. People who say chickens smell have only been around dirty poultry operations. Also, some people do not like the smell of barns, livestock animals or farms. Hmmm, these same people have no problem with a multiple cat litter box inside their house. Go figure.
Here is my experience. I have kept bantams and never had any bad smells. Then someone gave me 4 black jersey giants. Shew-wee!!!! Those things smelled worse than pigs! I gave them back. Pretty to look at.....nasty to the nose. Don't know if it was just that breed or standard size chickens in general. But my bantams are sweet and clean