Hexdrinker*
Hextech Gunblade and Revolver are AP items tyvm.
And I hope you realize that Veigar is best used as a counter-pick, not a first pick. Assassins in general, especially ones with mobility like Yasuo or Zed shit on champions like Veigar in general, who sit around as niche picks. Telling me Veigar is bad because Yasuo and Zed counter-pick him devalues your own argument, because they were good against Veigar already.
AP Mages will frequently lose to Veigar's, especially good ones. It's a losing lane match-up, they have to build AP since it is how they will scale their damage, so the best one can do is hope for ganks to gimp him as hard as possible before he drastically scales.
Once you hit late-game, the little rat is still going to ult one of your squishies and chunk the shit out of them.