You don't really have a lot of options.
The glass roof doesn't provide a ground plane, so efficiency of any antenna you mount up there is going to be an issue.
About your only rooftop option for a permanent mount is to go just about the 3rd brake light, or maybe up front.
The amount of ground plane is going to be limited, so higher frequencies will have less issues. If you are planning on VHF, VHF Low, or CB, you'll have a less than ideal ground plane.