Thanks for your response, but I still don't understand. Let's say for simplicity, I make the mass of a circle equal to the area times a density value ie mass=(PI*r*r*)*density. Now, I am not sure how to get a proportionate moment of inertia value. The circle is always in world space.
Also, an OBB which is in local space, but gets transformed into world space every update step could have a mass of widht*height*density. How do I get a moment of inertia value?