I have about 6 inches of litter in my coop. Probably started out as 8 inches, but the chooks break the big bits down walking on it. I try to rake it every week, but don't always make it. My coop is about 4x8, and I can put most of a bale of compressed wood chips in it to start with. Then I top-dress and rake it when it gets funky. Raking it when it's cold outside puts more air into it for better insulation value.
I emptied it out when they were spending the snowiest part of the winter indoors all day, and tossed the old stuff in the run to cover the snow/ice to lure them outside. Worked okay, but the run is really deep now with wet-ish litter and mulch from the city "tree dump" shreddings. Unfortunately my one decent compost bin is full, so I'll be emptying the run into some kind of improvised compost bin - like a hoop of hardware cloth or maybe that piece of expanded-metal plaster lath I have left over. . . .
The true "deep litter method" is somewhat wetter than we're using in back yard coops. It works in large coop-barns with very large air volume per square foot (higher ceilings), massive air turn over, and some amount of heat. If your litter can "decompose" it's too wet, and you probably have ammonia issues. The "deep litter method" most people here describe is more dry; the litter absorbs the moisture and helps it evaporate before ammonia can form from the urea (white part of the poo).
I was thinking a few weeks ago that I would need to change my litter soon, but the more I look at it, the more duty-cycle I see left in it, especially if I top it off regularly with fresh litter. I think I changed it last in December. I'll probably change it out in a few weeks.