Well, I'm at a bit of a loss, because I've never housed ducks before! Other than a pool outside, I'm not sure what accommodations ducks need. You probably need to plan an area for them to sleep on the floor, rather than a roost.
Do you have a budget for how much you can spend? Do you have any tools, like a saw, hammer, etc.?
If you look at the very top of the page, there is a link called "Coop Designs." You can look at some of the coops there, to see if any appeal to you.
For just your duck and a silkie, you could probably even modify a dog house. Or you could build something larger. Do you think you want to get more chickens or ducks? Also, what area of the country do you live in? It helps to know what your weather is like.