You first create the body, and then the geometries.
You create the body as you always do:
Body body = BodyFactory.Instance.CreatePolygonBody( ... )
and when you create the geometry, you reference the body in the arguments:
Geom geom = GeomFactory.Instance.CreatePolygonGeom( ... body ... )
I omitted the rest of the arguments, ... means the rest of the arguements. To use a single body in several geometries, you simple reference the same body. You can put an offset on the position and even an offset in the rotation relative to the body. Take
a look at the arguments in the CreatePolygonGeom() method.