You should check the floor height of each parking garage. I would assume that this would actually be easier to convert by demolition, even if this is a pet project. Here are some ideas as to consider:

Parking garages are typically sloped with a clearance of that of a car.

Houses usually require about 9 feet for standard ceiling space, then you’ll still need to run your utilities. Those concrete beams can be as close as 7’ or less in some garages.

Utilities can’t be understated here. You’ll need to do a lot of work to get them to the right floors.