Who builds garage apartments? Budget?

[Bruce Hansen]

Trying to price out contractors that build over existing detached garages. It’s hard to find. Ideally I just want the shell built and I can finish out the inside myself. I also hear that sometimes building a garage apartment over an existing detached garage may require additional stud shoring as well as underground structural piers. Does anyone have experience with garage apartment additions? What problems did you have? What was the final cost?