Well...to my uncreative eye, it certainly looks like this house had a garage or carport once upon a time, and somewhere in history, the garage/carport was turned into habitable spaces and made part of an enlarged house. Perhaps done by a creative designer.

So the first thing to do is to check with the local zoning administrator to see what sort of parking requirements are applicable to this property. As it is now, it may be nonconforming with the zoning ordinances and not saleable without a conforming garage.

While at the zoning administrator's office, find out what the setback requirements are for the property, and where the buildable envelope for the property is located, it's dimensions and size. If a new garage is desired or required it will be important to know how much space (and where) for the location of a new garage.

Then talk to an architect. Or you could pay an architect to do all of this for you.

But be sure you work with a "little more creative" architect...