Q: Baleful Strike - Active: Unleashes dark energy at target enemy dealing 80-260 (+0.6 per ability power) magic damage. If the target is killed, Veigar gains 1 ability power.
Passive: Veigar gains 1-5 ability power when he kills a champion from any source of damage
W: Dark Matter - After 1.2 seconds, dark matter falls from the sky to the target location, dealing 120-320 (+1 per ability power) magic damage.
E: Event Horizon - Veigar twists the edges of space around the target location for 3 seconds, stunning enemies who pass through the perimeter for 1.5-2.5 seconds.
Ultimate: Primordial Burst - Blasts an enemy champion, dealing 250-500 (+1 per ability power) plus his target's AP in magic damage.

the main reason that i decided to show this build is that i see to many bad veigar players just gettting a mejais and then getting shutdown. hopefully this build will teach people that there are other ways to play the tiny master of evil

The reason for the seals is as you can see there is jack all mana regen. as for the marks with this build you can switch out the void staff for more AP or some armour or magic resist.
The quints and glyps are to help get the early farm with baneful strike and to help late game with the scaling AP.

i go for a 9/0/21 build picking up the mana regen and ability power + ability cooldown plus evan moore magic pen this allows veigar to nuke tanks with deathfire grasp.

The death fire is THE CORE ITEM of this build to run this you will need all of the runes and Masteries. so you start with dorans ring to allow you to extend a little to get that 1 minon with baneful. after that go straight for the shoes because if hey have a jungler veigar is extreamly prone to ganks. then go for the death fire grasp but go for the pick before the codex because of the gold per 5. then either if your are doing well then you can go for the soul stealer otherwise go stright for the deathcap this now allows you to kill most people from there i recommend the void staff cause they will start to try and protect themselves against you. the archangels is a great 6th slot due to the massive amount of ap it grants you at lvl 18.