There are some rules, as far as the weights, they always go in the back, that means they have further to "fall" and thereby transfer more energy to the car and all that = more speed
There are dimensions on the width and height off of the ground, other than that, its a free for all on size. I am thinking of using the plastic shell form the toy collection I bought months ago. There are some that are about the correct size as a template. Should be fun! I will post up picks.
They are also doing a parents race, to let the dads do what they want!