DI or piston?
You are missing the gas rail, charging handle, your various nuts springs and screws, dust cover, and flash hider I believe. I think I saw a gas block image up there, if not then you need that too.
http://www.columbusracing.com/forums/showthread.php?t=92078
This thread is perfect for finding out what you need. He did a great job listing all the parts you need to do your own build. If it's not on this list, you're missing something.