Might want to rethink your theory - in MN the vast majority of round bales are stored outside. Some covered - some not. A person that knows how to stack (my husband, BIL, hay supplier) can do so in such a manner that we do not have issues with maintaining the quality of our hay.
Hay spoilage in rd bales is lessened with net wrap, multiple layers of twine, etc. Many times and in many climates, spoilage loss in the winter is not severe due to frozen conditions and "dry" snow.
You will not have a premium hay product - don't care what part of the world it is in - stored outside! The producers who want top prices put the hay in sheds! Putting the hay in a shed does not mean it is a premium product, it is just a better way to protect a premium product.
In any part of the world when you have conditions available for hay to mold - moisture and moderate temperatures - your hay does not need to be outside for more than a week! You can stack the hay in the hay mound any way you want to, but when you start feeding it, the outside protective layer of the hay is ruptured and the inside is exposed. You will cause trouble for yourself if you leave this bale in a feeder for more than 1 week.