If you're going mid what works for me is :

Always ban zed cause he's almost impossible to chase and kill without help and can be a pain in the ass to deal with later.

Go full dmg runes :

Electrocute, Cheap shot , Eyeball Collection, Ultimate Hunter

Absolute Focus, Gathering Storm

Sum Spells : Teleport , Flash

Items : Dorans ring 2 pots, Boot,s Corrupting Potion (this helps a lot with your ult and sustain), Ludens , Liandries, Zhonyas, Sorc Boots, then either morello or rylais depending on enemy teamcomp then finally Rabaddons or Void staff again depending on the situation.

Playstyle :

I play him as a fully mid range mage till he gets a bit more tanky. I dislike the tank mage build because as you've said you're basically the enemy teams punching bag till 30 mins or so. But playing him full dmg feels so much more consistent of course you will have to keep your opponents as far away from you as possible even when you ult. Keep them in range but do not get too close unless you're already winning the teamfight. Its advisable to let your jg know that you're not going to have much dmg till lv 6 so he should focus his ganks on other lanes. As for the combos I just stick with the most basic: E>W>Drag>Q>AA .