Veigar can go both top or bot, it is entirely up to you. Though if you go bot, you will most likely stalemate the lane until you have DFG and Ult to combo people to death. Either way i suggest CDR+Spell pen because he has really good damage, but atrocious CDs. He is more useful top where he can make enemy casters think twice before engaging and provide an AoE stun, and then late game he can generally disintegrate just about anyone, but then promptly dies to anyone with a gap closer or ranged cc.
My recommended skill ordering
Bot: Can you harass or farm Q safely? Yes:QWE, No:WQE
A lot of skill is require with Veigar as positioning is important and hitting people with the edge of the Event Horizon then pressing W>DFG>Q>ULT>Q as fast as you can, then getting the **** out of there. He is not a forgiving champ to play on Dom but very rewarding and fun. Expect to die a lot and get guff from teammates, but hang in there. I have made people taste the rainbow with my Leprechaun skin and loved every minute of it, win or lose.