I've attached a 3D rendering of a modern home I currently designed for a client, to possibly give you more ideas.

Extending the garage down the driveway will almost create a "L" shaped house. But nowhere have I found something similar on house to give us a visual.

The added on garage won't really be connected to the house, in that you would not want to walk from the garage thru the new bedroom.

How about a free standing parking structure on the property somewhere? Is this lake house just for summer use?

Would a new garage work on the other side of the house? Or put more into the back yard? That might look better visually.

Turning it 45 degrees looks better.

I agree with pcmom. I like the look of the 2nd image. Here is another one, a little more modern-looking

How about if you build that bedroom above the existing garage? But make that a drive thru to the two car garage in the back. That would be great extra parking for guests.

Did you check local setback requirements?

and in addition to set-back requirements, if considering pcmom's suggestion, you will need to look into height restrictions, if any apply.

Set back requirement is 41 feet from road. That would give us roughly 11x13 4th bedroom (the current garage) and a 24ft long garage which could house our boat during low lake levels and winter. But I agree that a entry from garage to a extra bedroom would be funky. I guess building up is the only solution. Height requirements shouldn't be an issue there are lots of tall houses in our neighbor. Now I guess I need to get a visual for a 2 story or something detached. ugh.