Overkill for ducks. A fenced pen with a small night box that is predator proof. Doesn't need to be tall, think a dog house with a door and maybe a hinged lid for cleaning. Ducks don't need protection from rain like chickens. You need 1 ft. sq. ft for mini's, 2.5 square feet for light to medium ducks and up to 4 square feet for large breed ducks ( per duck). and that is just for overnight. They really don't need a house, maybe a windbreak. or lean-to if they have a fenced predator proof pen.
You need somewhere safe a dog, fox, RACCOON can't get into or climb, or dig under. A hotwired fence top and bottom takes care of almost all predators except possibly owls or hawks, eagles....
A net on top or roof would fix that. You can get a dog kennel, but would have to put hardware cloth around the bottom 2-3 feet high so raccoons can't pull their heads thru. (forget using chicken wire, it's worthless against predators.)
I mean , if you want a fancy house, sure they like it better with a moat around it....
But they don't roost unless they are muscovies, mainly it needs to be easy for you to clean , and if it is the night pen , safe from all predators.... so they aren't 'sitting ducks'.....
But they can't stay in that all day and night....certainly not 4-6......unless you want to clean it twice a day, assuming you are using straw or shavings which will get expensive...... consider rubber mats or pond rock or pebbles you can hose,out. Ducks have to have water while eating and they dunk their food in it, and they splash it and they put things in the water (leaves, rocks, food). They may try to swim in their water buckets...etc.... I have 23 in a rock night pen (temporarily, while making new pens) that is 12 X10 and I hose it daily or EOD.... I keep 4 runners in a 8X3 rock pen and need to hose it every couple days....Since I started feeding most feed in morning instead of evening they poop less at night
Ducks just need a safe fenced area, nothing can get into.You can use Rubbermaid bins, cut down in front for nesting boxes ....They don't like to stay indoors really.........