i wanted to build one too, but for me it wasnt worth it. i had an micro pc with a dc to dc psu. a colored lcd screen some usb gps and stuff like that. its hard first of all to integrate it well enough in a way that its going go be user friendly. so for me the best way to do it was buy an old laptop, comes with a car charger and some wireless audio transmitter so that u can use it with ur existing radio. just a suggestion thou from experience.