Part of coop cleanliness is design. Ventilation is key.
I have an 8 x 16 coop (128 sq ft) with 4 windows and a turbine vent besides the man-door and two pop doors. I also have full length soffit vents along soffit, front and rear. Floors are OSB with linoleum glued over that. I never keep any water inside of my coop. I never keep any feed outside. ( They do get treats twice a day, outside in their run. Run is 1900 sq ft ) End windows are sash, full open all summer long. Nearly closed in winter and closed up if temp below 30.
Dropping boards are 2 ft deep X the length of the roost poles. Smooth texture. Roost poles are 1 ft from the wall. (salvaged kitchen counter tops are perfect poop boards) I turn the inmates out each AM around daylight and I immediately use an 8" drywall finish knife to scrape the poop into a plastic Tote Box that I keep under one of the poop boards. My total cleaning time each day is under 4 minutes !!! (4 poop boards to scrape and whatever I see on top of the litter, which is very little because mine stay out in their rainy weather place which greatly helps me keep the coop smelling good) This is a fact. It is all I do to clean my coop year round. Every April we toss out all the old dried grass litter and replace it with fresh stuff just cut the day before. We both wear masks to do this chore and devote 3 hrs to it, including washing the 4 windows and knocking down cobwebs. We add to the litter all year long and keep it nearly a foot deep. I empty the poop box about once a week for my 10 pullets. I blast it out with a garden hose and allow it to dry in sunlight before sliding it under one of the poop boards.
I use only grass clippings year round and I keep them 8" to12" deep year round. I add a lot in around late Oct since I will not be able to get any more until March. They do a super job year round, and they are free !!! :-D I love the dried grass smell when I come in to gather eggs in the mid morning and afternoon!
My coop never ever stinks. I can smell poop in the AM when I first walk in, so I turn on a box fan at the west end and it sits against a window and pulls in fresh air for the 4 minutes I am in there. I leave the man door open too. Time I leave, no odor at all, and I shut off the fan. Warmer days I leave the man door open all day long to help cool coop, and if going to be 90 degree weather, I will turn on the vent fan around 11 AM.
This has worked for me for 8 years, so it will work for you too. I never clean their run because it is 1900 sq ft and is 65% shady too. So there is enough room that it never gets bad, and rainy days wash it down perfectly. It slopes, so no mucky puddles anywhere.
A covered roost for a rainy day hangout is mandatory to keep a coop clean smelling. Mine all roost under the east end of the coop on the rainy day perch I nailed up underneath. Works like a charm!!! You can make a perch and cover it so they won't get wet. They will congregate there on rainy days, and that is a hell of a lot better than having them indoors!
Keeping chickens is very easy provided a bit of forethought is exercised and some practical design. Easiest livestock to care for or I'd not have them in spite of the great tasting eggs.
Gerry