Zhong Kui is a beast^^build (Mid)

So for early game is it mana the key because ZK has a heal. (1,2 combo)
For the game himself always keep you passiv up.
For tower camper poke with your 1.
For teamfight for most of the time go in with your ultimate first damage to all enemys an heal for your team and you get either a kill or a active and that´s worth because of the low cooldown.
What i also like do to is pop ultimate and than sanctuary.^^

Pros:
Tanky
A lot of health (2780) lvl 20
pretty good damage. is say so every time i play him in ranked 10+ kills are standart

Cons:
i would say not max damage

The build is pretty simple, Warlock sash for hp and then the big change is void stone i think because most likely your opponent as mid-laner is also a mage and with this item u get magical protection a little penetration and power.
For the next item rod of tahuti or cooldown plate. i would say breastplate when in your game more team fights happening or the jungler (when physical) invates you often.
And the rest casual mage build
u can change the pen-item when your team has enough pen.