Design an App Mockup

I need some design ideas for an app. The app will allow cars to be sold on an Ipad and or iphone. The screen presentation must be intuitive and easily navigated. It would begin with type of vehicle eg 4WD, sedan, convertable, hatch then lead into model seletion then colour then trim then accessories find finally a summary Ideas are open to interpretation Idealy there would also be a desktop version which would provide addiotional functionality including trade-in's, finance options etc. The ultimate aim is to get a customer to select through the ipad/iphone (or android), the type of vehicle they are interested in. This is a basic interface. Place the tablet onto the desk where the pc screen is the surface of the desk. This would pick up the selection and the salesman can continue the sale on the desk. The salesman can then sit the customer down and using deskstation with drag and drop capabilities complete the sale.