It has to be realistic , can have anything you want as long as it ***LOOKS*** realisticly possible. That means whatever you build must have good g control, and must have the support strenght to ***appear*** to hold it up in real life. [:D] I hope that helps! You can have never done before elements, how do you think coaster manufacturers came up with their elements? They weren't made before so someone invented them [;)] OK I hope that helps!
WWS