Step 1: Design
The other considerations after that are the wheel size and the distance between them. With that template in place, it's car time! Here you can go nuts. You can make the car look realistic or abstract. It can have a front and back or be symmetrical. Here I'm going for abstract and symmetrical, but you can make your car any way you want.
The image here shows the layers of wood all stacked up over the wheels as well as all laid out for a cutting file.
Step 2: Cut and Assemble
The parts needed for the rest of the car are a couple of 5/16" bolts, spacers, locknuts, and a set of wheels with bearings. The wheels here are luggage wheels with ABEC-1 bearings inside. Inline skate wheels also work although they'll be a little bit bigger.
The assembly here is pretty straightforward. Run the bolts through a wheel, a spacer, the car body, another spacer, another wheel, and a lock nut to cap it off.
After this the car is ready to roll. This is when you can see if the design is what you want. You can change a layer or two or maybe even do the whole thing over.
If you're ready to lock it down more, then you'll need some glue.
Step 3: Glue!
Now you have a toy car that's ready for a ton of abuse.
Step 4: Car
There's also plenty of room for further customization. Stain or paint can liven it up as well as extra details such as names or stickers. Again, totally up to you. Make your own car what you want it to be!