I don't know ducks -- best ask about their winter needs and nesting needs on the duck section of the forum.
All birds need excellent ventilation and @rosemarythyme gave you good advice about soffit and gable venting. But don't let the builder talk you into those little louvered vents.
All birds need excellent ventilation and @rosemarythyme gave you good advice about soffit and gable venting. But don't let the builder talk you into those little louvered vents.