Hi there,im not sure u quite under stand your problem but  i rate it comes  down to basics,first of all you are going to need dimensions and you say you must draw the car inside and out,so i rate you must get someone who has a very basic car,get a measuring tape.then you measure and draw as you go on.if you want to draw a 3d model its going to be easier to first draw 2d drawings of the car and afterrwards use those drawings to draw up your 3d model. good luck