I'm not sure how they do it on the other side of the pond, but one of the big three does it like this: Dealer make orders, the geniuses in sales figure out who is ordering what options. Orders (custom or whatever) get sent to HQ, HQ then sends orders for cars to the plants. At the plants, there is a magical printer that prints out 'lablels'. These labels show how to build a car. They slap a label on a frame and away it goes... built to order. I know this because when the printer stops printing (mostly due to network problems) our guys got frantic calls to get the network link up so that magical printer keeps on printing those labels!! When it comes down to it, it's a pretty simple system: You place an order and factory gets and builds it... end of story.