May i request building instructions or build pictures for the car? I find it to be quite a challenge to fit two people comfortably, side by side, in 6-wide cars.
It really depends on what wheels you use, if your cars fits minifigs or not, and what type of car you want to make. All i can say is, you need axles and wheels(duh), cheese slopes, 1x2, 1x3, 1x4 plates, 1x1, 1x2, 1x4 plates with no studs, and grills.