I would header the wall off opposite the door about 6” off the floor. Cut the 6” space out of your sheathing. Cut a piece of pressure treated plywood the dimensions of the floor and slide it in. Then replace the sheathing. Trim the opening out with a removable panel.
Then, when its time to clean the coup, you remove the panel, slide the plywood out, shovel and hose it off, then slide it back in.
Clean chicken coup in 10 minutes. Works great on mine.