I would like to know what the space for two ducks inside a fenced area needs to be. Or what you would recommend knowing that ducks are messy. If anyone has an idea for what they would do, have done, or would suggest please let me know.
This might not sound very helpful, but I would suggest making it as big as you have the room for. One reason is that you never know if you're going to have more birds in the future. The standby suggestion is at least 10 square feet per duck, but bigger is always better. A large run is easier to clean, and you don't have to clean it as often.
The run we built for my ducks is about 15 x 25, so we have more than enough space for our 5 ducks. A few years ago we had a smaller run that was long and narrow, and it was a disaster. There wasn't really enough room to move things around, and it got so messy.