I saw on trucks this weekend how easy it is to make your own diesel for a fraction of the cost, i was just wondering if very many people actually do that, and how safe it was for a newer truck with some performance mods

Some do and some don't - for various reasons.

Try a search on this website, its been discussed many many times. You'll have to select all forums because they're spread out over the various forums.

Biodiesel thread:
http://www.dieseltruckresource.com/dev/showthread.php?s=&postid=743405#post743405