I have four ducks and they have a dog box in the pen. I do not have pictures because this is a temporary pen made from free pallets with wire nailed to the pallets. It is big enough for the dog house, a baby pool and for them to walk around. I have wire across the top so nothing can get in.
It is not pretty but the ducks are VERY happy for now. I get them out each morning and evening to eat grass and play with my supervision.
As a new Duck "Mom" I worried the first couple of nights so I would block them in the dog house in the evening and let them out to the pen during the day. Now if it is windy or they are not happy with the weather they go into the box. It is their secure place.
I like for any animal to have the option of shelter if they choose.
The dog box will go with them when we build the new pen. The roof lifts off for easy cleaning. We are going to put hinges on it so it will not blow off in winter. I put shavings in the box and a layer of hay on top. When I clean it I usually just have to remove the layer of hay and replace with fresh