I would hire a local architect to explore the possibility of doing what you
want [and other options he/she might suggest].

You may or may not have structural issues with the lower floors, etc.

Sometimes an extra support here and there will allow the addition, other
times it is... "This is not going to work!".

If it is reasonably possible, ask for a ballpark figure for construction,
permits, etc. Don't forget about upgrading electric, water, air
conditioning, etc. (if necessary).

Then say go ahead and draw up the plans, I'll wait, or I'll pass on the
project.