I've never built one. Seems fairly straight forward. I would recommend using ridge vent as it would be much easier, but a cupola would look really nice.
I agree ridge vent would be easier, but we have two cupolas on the barn, and Bob read somewhere this morning that a cupola is the preferred ventilation method for a peaked roof when one has chickens, and he wants to get it right. It will look nicer, and maybe I'll even get a neat chicken weather vane out of it when all is said and done
