Ducks have very short legs, most of them don't fly at all or only a foot or two off the ground and nest on the ground. They need to be herded in every night. Ducks are very sensitive to light and don't really sleep at night. If I get home late I often find mine browsing back and forth looking for snails, slugs or other delectibles and actually seem more alert at night than they often do during mid-day when they seem to be most likely to be seen resting on the ground, maybe with their head under one wing. If you have neighbors and noisy ducks if you can't be there at the crack of dawn to let the ducks out and can't herd them in EVERY night then I recommend you pass on the ducks.
Ducks are very vulnerable to any kind of predator, coons, skunks, possum, coyote that finds one nesting at night. If they find one they will probably find the rest and you could go from many to no ducks in a single night. The shelters have to be something stronger than chicken wire mesh at the ground level as some predators can tear it apart or reach in to pull whatever they can get their hands on through the cage eating everything they can pull through the wire amputating what they can't kill. A coon can easily reach though 1" chicken wire and snag a little fresh meat. 1/4" or 1/2" hardware cloth at least two feet high with a bit of an apron (2-6" bent and lying flat and down on the ground") will help keep a predator from digging in or reaching in and snagging one of your animals. You might consider putting a bottom on a ground level enclosure but I found they make it hard to clean and can be a source of disease. The best source of information I have found about duck breeds on the Internet is http://www.metzerfarms.com. If you are planning on keeping ducks I would read all about the breeds they have and sign up for their blog.
My primary coop is a rectangular box, 2 feet off the ground with a 1” thick floor that is covered with a waterproof piece of shower liner to keep wetness caused by the birds from ever touching it. The coop has a pitched flat roof that rests on one end and is higher on the other where my chickens fight to get to so they can see out and have the the fresh air. This was very simple to build and wasted no wood because the walls are made from three pieces of exterior siding, one of which was cut in half for the ends.
Over a dozen chickens have chosen to crowd in that coop rather that the larger one with more space and air even though only about half of them had the coveted penthouse roost. The roof is 12 foot long metal roofing material that creates enough of an eave on both ends that water never comes into the top of the coop and you can stand under it to collect eggs etc. in the rain without getting wet. The bird(s) that are on the lower roosts are the first ones out every morning when the automatic coop controller opens the door for them. If you put ducks and chickens in the same coop, I recommend that you don't, then you need to have enough room keep the ducks from having to sleep under the chickens. The chickens poop a lot at night and take up the entire vertical space from the floor to where they are roosting because of that. We built our coop raised off the ground with a floor and a hardware cloth enclosure beneath to shrink the footprint and to provide another 32 sq. ft. of additional shelter for feeding or sleeping. This winter we kept our ducks in a lean-to type greenhouse to help protect our citrus collection. They did a very nice job. Instead of losing citrus or having to bring the citrus inside the citrus grew outside the house all Winter.