Hi!
Welcome to BYC! Wow, you have a lot of animals! I have a suggestion. If you want bantam chickens, why not build a walk in coop that is large enough to divide off a section for your eventual ducks? I think a shed conversion could work, then you are on your way to both additions. I know the two have different needs, but seems to me like you could divide a shed in two and have two completely different set ups in each side. You could also have two separate runs for them.
