I also agree with Alec. I have made 2 clocks for my cars, whenever I have bought a car without one that didn't have anywhere to put a bought one easily. Then it was a matter of making a clock to fit a particular place in the dash and I know from experience that you can end up spending enough to buy a dozen form the car shop!
If you really want to make one (to fit somewhere) let us know and what type you want i.e. LCD or LED etc.