Karen - don't build anything, just look for a cheap or free doghouse! A plastic one is even better because you can hose it out. Since they don't roost, they don't need a tall structure. Don't need tall fencing either - probably 2 feet would hold them.
They are not as prone to disease like chickens, and the care is no more time consuming than chickens. My chickens do just fine in the cold, and I'm sure the ducks will do just as well.
And - they love, love, love the wet weather, unlike chickens!
Also - the food intake difference is astounding. I have 6 ducks and they are taking about a month to go through a 50 pound bag. However, I was feeding crumbles and they waste alot. I switched to pellets to see if it slows down even more, and I'm going to add in some whole grains or scratch and BOSS.
The chickens rarely leave the feeders even though I only feed one scoop twice daily. :/
Mine are on the verge of laying, I can't wait!
I have to go get the kids to school. Be back soon.