Parts list i sent a friend on youtube, For a 6 channel traffic director.
Ok, to start you will need:
Either 6 or 12 of these puppies (whichever you choose) Bulkrate is your friend, it is a wholesale discount, it depends on the amount of a piece you are going to buy, just remember "APPLY BULKRATE DISCOUNT"
http://www.dealextreme.com/details.dx/sku.2395 (White)
http://www.dealextreme.com/details.dx/sku.1776 (Red)
http://www.dealextreme.com/details.dx/sku.1775 (Blue)
Now we need to power the leds without OverVolting, thats where the drivers come in, you will need 1 per each channel regardless. Just Desolder the pegs and put wires on instead to your 12V (can power up to 3 leds in series)
http://www.dealextreme.com/details.dx/sku.13557
Finnaly, the most important part, Optics, if you use shitty eBay lenses the light output will be cut almost in half compared to my new ones. The best lenses i found were on ledsupply.com, i used the oval lenses for the Cree XP-E, they create a HUGE beam spread with an intense amount of light. I wouldn't use anything else!
Lens:
http://ledsupply.com/10197.php
Holder:
http://ledsupply.com/10736.php
Use a piece of angle alum to mount on 1/8-1/4" thickness for heat dissipation .
To build this product you need patience, first of all DealExtreme is a Hong Kong based company, which will mean it willl take 2 weeks before its at my door. If you want the quick/expensive route use ledsupply (7.49 per vs 2.80 on DX)
If thier is anything i missed just get back to me and ill help you as much as possible!
EDIT: a second thought you should go with ELS, he can sell you all the parts in one