Yeah, i know, but I think this build is good for start, and when you play some champ longer, you make your own build, becoase you know what you need... So this is "optimal start to your Vel'Koz carrier"

You really should rework your Itembuild.
DFG is bad on Vel'Koz due to his low range and the fact that Vel'Koz isnt really a burstmage.
Its also arguable, whether it is a good idea to rush Rabadons. Yes u can go for it, but a finished Grail and a Void Staff or Linadrys (which you didnt even mention...) really do a better job, cause Vel'Koz hasnt high AP-ratios and is really much reliant on landing 1-2 small combos and then go for a big one, so DFG wont work and Grail is better than Rabadons because of the CDR.