Flaring Truck Fenders

I have looked for some help everywhere on this site to make flared fenders for a truck. Like Baja style ones. I have the f 350 ford that I want to baja out. Some like this-

www.automotiveforums.com/vbulletin/showthread.php?t-419287&page=2&highlight=truck

That might not work but just go google.com, prerunner in the image search. You probably know what I am talking about but I don't know how to do it. Any help? Thanks, I have styrene and puddy I just don't know how to go about starting it..... Thanks guys