Humanly impossible, without modern engineering and equipment.
Well sure, but once you introduce the magic wand of Jellohoba then it becomes possible. After all he made polar bears and koalas fly over oceans to get to the ark. Why even make Noah build anything at all? Why wouldn't Jellohoba simply make an ark appear already built?
Somehow, god always takes the most cumbersome and difficult path to accomplish anything. He leaves zillions of angels sitting around doing nothing, while making pesky little humans struggle to do anything.