Full-blown clean? Never. Okay, twice a year. Haven't had my chickens more than 8 months yet, and only cleaned out the litter earlier this spring.
Every week, I rake up the biggest poops from the pine shavings (Deep Litter Method) into a bucket, toss that stuff into the composter. Every couple of weeks, I add more shavings. The chickens "stir" the bedding litter up themselves, so I don't even have to turn it. But I might, if I was feeling industrious at the time I raked out the poops.
I do add poultry dust occasionally, and toss some DE around, too.
I do more cleaning OUTSIDE of the coop than inside, as the chickens sun themselves on the low roof of one coop with its attached pen, and they poop all over it. The rooster uses that roof as his crowing station. He'll crow in other locations, but that's where he does the major wing-flapping, belting out the I'm The Biggest, Bestest Rooster In This Neighborhood crows. The girls get up there to look around, or perch on the edges of the roof, looking outward, so of course they poop on the roof.
And the run needs attention, too. But the coops? Far less than I thought they would!
(But maybe I'm a trashy, messy, hillbilly kinda gal who has lower standards for chicken coop cleanliness.)