Build a two-story: The two most expensive parts of any house are the foundation and the roof. When you build two stories, you can double the floor area while halving the costly square footage of the foundation and the roof.
Put the garage in the basement; it is virtually free (if you live where there is slope to the land). In most parts of the country, people will likely build a basement anyway, so add a door and drive in. If you have a completely flat lot, this may cause trouble. Adding another structure for a garage could easily add an impressive sum to your project. Unless you have health reasons to avoid stairs, the exercise up the stairs is good for all of us.