I remember seeing this a long time ago and for some reason I randomly remembered it today. It's a BMW concept using polyurethane-coated Spandex on an aluminium frame replacing normal heavy body panels.
Wikipedia: BMW GINA
I think it looks awesome and probably isn't that difficult or expensive to do. For the bonnet you could use the standard frame and literally replace the sheet metal top with this material.
I just had a quick look for the material and it's not only quite cheap but is available in so many different textures/effects/colours that your car could be totally unique to your own taste (I imagine it would help if you had taste though)
Also, to further reduce the weight the frame could be replaced with carbon fibre (if MazdaRob can do that that is

)
Yes I'm living in engineer dreamland again!
Robert