Question
I want to put a garden where Bermuda Grass is right now.

Can I just start tilling and raking or do I have to do something before I till and rake?

Thank You

Answer
I'd kill the bermuda first.  Spray the entire area with   glyphosate.  With the cooler fall temperatures, wait about a week and then till the whole area.  Gylphosate does nothing to the soil so you can plant immediately after tilling. The bermuda may still be green, but it's dying and can just be tilled in for organic matter.
Bermuda is the primary lawngrass where I live also.  Why we would chose one of the most aggressive weeds in the world for a lawngrass is beyond me!
Jim