Cleaning a coop with 5to10 chickens is pretty easy. We do our coop every other week and lay all new litter down. Clean the poop board often and there is never a bad smell. We clean the pen weekly and my chickens are clean and happy. We do diatomaceous earth when we clean the coops every time. I could not imagine cleaning my coop every 12 to 18 months. The poop build up must be insane. Yuck!
Do a search of "composting deep litter method". The 'bad' poop accumulates under the perches of the roost where it's dealt with much more frequently.