My current aviary is 25x30ish ft. Currently using straw over a red clay floor. The aviary is partially open on top allowing the weather in. When it rains, the aviary floors turns into a muddy, smelly mess. The ducks obviously love rooting around in the muck, however, I don't think it is all that great for the chickens or guineas. And if we don't get numerous days of dry hot weather, it takes weeks to dry out.
At this point I am thinking of mucking out all the wet nasty straw and starting over with masonry sand. I can get 16 tons of sand for like $175ish delivered.. I was thinking about gravel, but 1) it is more money, and 2) I don't want to hurt the ducks feet. I know I don't like walking barefoot on gravel, soooo... I am thinking the sand will be easier to dry and easier to rake out the poo.