Insignia will only handle 2D and 2.5D toolpaths so if I am understanding your request correctly I dont think it will do the car roof machining that you are inquring about.
How are you going to be creating and feeding the 3D car roof into a software package? Will it be pre-created from another package?
AC Pro allows you to model and machine 3D pieces and parts so currently that would be what would be required in order to machine a car roof.
Let me know about the above inquiry and I might be able to assist a bit further.
Their is a very basic 3D milling package called Millwizard that may assist with what you are trying to do but it will all depend on the file you have to input/import into the software. Search the web for MillWizard if you think its something that might help your cause.