So now you have three cars. And you need somewhere to put them all. While the old one-car garage just isn't going to work anymore, beware the three-car garage in its traditional configuration (that is, three cars side by side). That's a lot of structure to put right next to your house, and it's not going to blend easily.
Garages Shouldn't Hog the Spotlight What should be the focus: your house or your garage? Sadly, many garages are given pride of place in a yard and then compound the problem with their size. Three enclosed car bays lead to a gigantic box that dwarfs its parent building when the opposite should be true.
Big Doors Are Ugly Car-size openings mean gaping maws right at the front of the building. Garage doors are then either ominously blank panels or, worse, overwrought with detailing.
Proportion Matters You can add only so big a wing before it loses any connection to your original home. The things that give your house character (moldings, window treatments and the like) don't work on something the size of a small Costco.