The challenge in what you are trying to do is that you can have multiple correct UML diagrams for any piece of code. Just trying to automatically get a diagram ends up with too much garbage when using most UML tools - and the tools just end up getting in the way.
We created Architexa to help in this situation - Architexa helps you to get to useful diagrams fast - if that means connecting to source code commits or even building layered architectural diagrams. A good discussion on some of the things that you might be looking for can be found here.
