EDIT: SORRY! I misread your OP. I thought you already had a 1 1/2 and wanted to enlarge it. Now I realize you are looking to replace the home not just expand the garage 
so my post is really not relevant.
We are in the final construction phase of enlarging our garage from 1 1/2 to 2 car. About 75% done. Putting 2 carts + car in it would be very difficult due to the fact the way the A/C system is in the back of 1 side of the garage. If the A/C wasn't there it could be don one behind the other. I REALLY had preferred a golf cart garage but due to the property setbacks there was no room to do that. It would have been a lot cheaper for sure.
Here are some photos of the process:
Dropbox - Garage - Simplify your life
Just to add ..... get LOTS of bids. Had over $10,000 variation in bids over 4 contractors.