The good news is ducks arent picky or need anything fancy. A properly ventilated plain box that shelters them from the wind and rain and predators is good enough. They dont roost, they dont need nesting boxes. Just a boring roof, floor, and four walls makes them happy, its a pretty easy build. Or if you want to be able to get in the coop too, some people just use sheds they cut some vents into.
Is there something in particular that hooked you on deep litter? I know some people swear by it while many others have tried and had trouble with it/didnt like it - just wondering what sold you on it.