The author of the book Enslaved by Ducks (read it here) says that ducks require "more maintenance than the Space Shuttle." In a way he's right--ducks are healthy and don't need shots, rarely fall ill, and in California don't take any special weatherproof housing, but they still require a good amount of attention.
The key thing is that they MUST be in a predator-proof pen between dusk and dawn. I used a commercial "build your own chicken coop" kit to make them a coop. I lock it with a padlock because raccoons can open the latch. The wire on the coop can't let a raccoon get its paw through, or it will reach in and mangle your ducks.
Ducks also need a good quality feed, which I get at a feed store. You can supplement their diet with vegetable and fruit trimmings, worms, and even cat food. Mine forage in the yard dawn to dusk, so they eat a lot of bugs.
Much, much more can be found on the wonderful duck site, Live Ducks