I have the car drawn, but what info does the a 3D art studio need to make a 3D model of my car?

What poly count range are you aiming for?
What file format do you want it in?
Do you have defined measurements?
Are they just modeling, or are they texturing as well?
What all sorts of texture maps are you wanting? Diffuse? Bump? Normal?
Does the car need to be rigged for animation? If so, how will you be driving the animation?