The biggest inconvenience is that ducks really make a joyous mess with water. You'll need two water sources; one deep enough for the duck to submerge it's whole bill and another for the chickens preferably where the duck can't reach it.
The ducks and even the geese will wander up the ramp into the coop if they're bored so you might not have to worry about additional housing if your coop door is big enough for a duck to pass through.
The ducks and even the geese will wander up the ramp into the coop if they're bored so you might not have to worry about additional housing if your coop door is big enough for a duck to pass through.