In the past, I have had Buyers looking at my listings who wanted space for their car collection. Normally this is a difficult property to find, especially on homes under $2m. However, this home has the PERFECT yard to give concealment to the extra garage space from the road as well as privacy from the neighbors.
In this mockup I have added a 30' x 40' (approximately) garage in two locations. The huge back yard easily accommodates this garage that is great for 3+ automobiles. Clearly adding a 4th or 5th would be easy to do as well with the additional space in the back yard. Plus one in the existing detached garage with a car-lift. In this plan, you could actually have "drive-thru" garages with a driveway loop through the porte cochére back around the existing detached garage. Attaching this garage to the existing building allows that back area to be "shop space" access.
Are you a car collector?
To give you a reference, I built a 30' x 40' detached three car garage but it is actually being used as my woodworking shop. (But the next owner of my home will love the 3 extra garages.) I had it built out to the point of being "dryed in" about 8 years ago for about $25,000. I completed the interior with house exterior siding so that I didn't have to worry about damaging fragile drywall and I could easily wash it down if I wanted with a pressure washer. It has an entrance door and three 10' garage doors. The ceiling height is 10 feet as well with dormers to make it cosmetically pleasing. I also have 3 skylights in the rear plus the dormers to let in light. When you build yours, be sure to put in floor drains so you can wash your cars inside.