I dont find this build useful in late-game. Because you dont have any defense except your stun and flash. And that isnt so reliable. A nice Zhonya's or Banshee's Veil is enough to keep you alive.
Also, Tear of the Goddess isnt a good item for Veigar, due to him lacking defence. Also, your mana problems can be fixed with m.regen runes, masteries, and the blue buff.

With the changes you made, I really like this guide. :)

Okay.

To add to Agoney's reply, your item section is rather dull compared to the rest of your guide. Try to spice it up!

Nice start, but you need to expand it a lot if you want to go anywhere. Look at my guide to get an idea of what to add. (ignore the MIB snipeing and such, talk instead about how to stun and such)

+1 though, good start