Here are a few pictures taken while making a recent car cake. Notoriously time consuming and tricky to make, but definitely a crowd pleaser!
I use ganache as a crumb coat to give a firm surface to work upon.
Florists' paste is best to use for wheels so they firm up nicely before attaching. Use a mix of over 1part florists' paste to 3 parts sugarpaste for covering the main part of the car, and make sure you have a can of confectioners' varnish/glaze spray (and in this case a metallic spray too), it makes all the difference to the finished product!