Cashflow is a foundation and extremely important,. 

Thats why I thought maybe building her a home where she never has to worry about old plumbing or electrical or foundation problem.

Typically doesn’t comply with footing/foundation requirements, vapor barrier in the slab, need to run water to the unit, you’ll need to comply with a number of electrical requirements, insulation, separating the garage space from dwelling and many other requirements.  

Other than a badly shifting foundation, which I don't like dealing with, there's virtually nothing on a house I can't fix.

Your posts should be more concise. not multiple.Go on line look up landlord law for your state and find out the laws to get a good foundation.

Foundation?

Is there a title for the home if it is on a foundation, or do you need a title at all since it is on land?

I recently purchased a single family house and am having a contract repair some foundation work.

If you plan on duplexing consider that because seperate entrances are key and to have to build a staircase down to the ground from above or cut into an existing foundation is a lot of $ needed to spent that can be avoided.  

Though we can finish most of the interior work, we are skeptical about foundation and framing.