Ah, decaling is much easier then. Did you find a template? I get 5 free per month, and I have 2 left, resets in less than a week so I doubt I'd use them. If you want I can d/l it and send it to you.
Templates aren't perfectly accurate though - Theres so many different models and trims. For the most part it's pretty accurate.. But it can be off by an inch or so in some spots. It's good if you don't have access to the car.
Since you do, you may as well learn the proper way others are mentioning! Cut a 12" x 12" square out of vinyl or whatever. Tape it to your car, step back so you can take a straight on, full picture of your vehicle... Transfer it to illustrator /corel, whatever you use... Make a 12x12" square, then resize the photo until your cut vinyl square is the same size.
From there, you have a pretty good, almost perfect template. Even if you go the template route, I'd suggest following the above steps... it's great to learn, and you can compare it to your template to make sure it's accurate.