This is an awesome setup,and needs to go here. https://www.backyardchickens.com/t/...ing-summer-2012-20-byc-store-gift-certificateYou could do something like our "Fort Dux":
(Please excuse the mess - the projects never end.)
It is enclosed in welded wire fencing on the top, sides, and 3 feet in along the bottom.
In addition, the sides have three feet of hardware cloth along the bottom to frustrate the raccoons and their grubby little paws.
Although we occasionally let them out to forage and probably will do more of that in the future once the whole garden area is fenced, they spend almost every day in the fort. It is 28x16, which I figure will house a maximum of 36 ducks. The goal is to keep the laying/breeding population at 12-16, only rising above that when we are raising more ducks for meat.
They seem perfectly happy with the accommodations. They spend most of their time outside, going into the shelter only on warm, sunny days.