Good luck with that! My friend in Washington DC is replacing a single car/single story garage with another Amish pre-fab one. What a pain in the butt to find an inexpensive solution to having an architect draw it, stamp it, etc. all for a pre-fab shed that will sit on a slab. And there's still a hold up of some sort. If you have visions of enjoying your deck before winter returns, I'd suggest biting the bullet.

Dormers are essentially required for attic (in the roof) square footage. I am not a building code expert but I am pretty sure that bedrooms require windows, assuming you want bedrooms on more than either end of the house they require dormers. As to your first drawing, houses similar to that (I forget the style) can be very striking and are very nice. I am not sure that they are cheaper to build than just going straight up, especially in Minnesota wher the snow load on the second roof is going to have to get transfered down to the foundation. If your plan has walls that will carry that load then it might be great, but that would essentially eliminate an open floorplan. I would think that the additional bracing required to have an open floorplan, modifications to the roof (essentially turning one roof into three), and the additional complexity of the plan would significantly eat into the cost savings that were the whole reason for the lesser square footage. Looking at the floorplan, I am assuming Lauren doesn't mean adding square footage over the garage roof, rather, building a second floor on most of the first floor (all that is not covered by the garage roof) and putting some additional one floor only square footage under the roof that also covers the garage. I think that would be fine, especially, if you can get the garage entrance turned sideways.

Am I misunderstanding about adding two stories to an already two story house? What does your township or city have to say about such a tall home? That is a massively expensive undertaking as well. And yes, it will require an architect.

I'm not an architect, but I agree with Mark 100%. If your garage idea isn't the answer an architect will have a better one. They will be familiar with local codes so they'll know what you can and can't do. There is no sense in planning to spend a lot of money without good planning. You don't need to take ideas to an architect. Tell them what the problem is that you're trying to solve and it's their job to solve it.