You can add several materials to a single object. In your case, I'd add a glossy black material, then select the window faces and apply the glossy black (I'd not use a glass material, as there's nothing inside the model, and transparency is slow to render).
The same applies to all parts of the model that should have a material (or surface texture) that differs from the main body (like the undercarriage, the wheels and details on the main body).
To add a new material to an object, click on the "+" button next to the list of materials, then select the new (empty) line and create a new material.
Then select the faces in your model to which you want to apply that new material, select the new material and click the "apply" button.