I did a couple of atttached "carriage garages". The homes where 2car side entry, and I built a single car attached that you would basically drive straight into. There was a small pass-thru that connected both spaces.
The main thing you would have to consider is- do you have enough space to build? That's not the amount of room to the property line, but the amount of room within the "building lines". The next biggest hurdle is the HOA, if there is one. Getting approval from a board of people who usually know nothing of building/construction.
Other than that, it a matter of size, design, and price.