hey, i am not a modeller, but ive seen a couple of tutorials for car modelling and use the same technique.
First you have to know what you're modelling (which you do) lol. 2n, you need reference images...plenty of reference images. 3rdly, you need blueprints of your car. A view from the front, the side, back, top and bottom. (These need to be the EXACT sizes and match up. You can scale and trim in photoshop)
Its not neccessary to have every view, just front, side and top but hey, the more the better.
Upload these on to image planes or planes in Maya and position these planes accordingly. Now you're ready to begin.
Like i said, this technique is based on what ive seen so it is time consuming but if you're a modeller im assuming you have patience.
1) Using your image planes form the outline of your car using nurbs curves.
2) Now Start with a car door or a good starting place of your choice. Create a small plane, (square shape) and extrude the edge. and again, and again and and model this way.
This is an extremely painstaking way of modelling but yuo can get some awesome result. Before attemtping, i'd invest in some vid tutorials (Digital Tutors have some amazing ones for cars)
good luck
those who succeed are only the failures that never gave up.
https://www.vimeo.com/7080130