here is my frist guide about zac.zac is tanky jungle.he also uses ap so he can be ap offtank.

SPIRT VISAGE:Pretty usefull item for zac cause it ads healing to his pasive i think u should build it as early as posible.
WARMONGS s ARMOR:Also usefull item cause it give lots of health and lots of health regen,and in cobination with SPIRIT VISAGE it makes zac almost unkillable.
RANDUIN s OMEN:Gives you a lot of health and armor and cause of its pasive you can kill and endure more adc attacks.
SUNFIRE CAPE:Gives u moderete amount of healt and armor and with its passive u will deal magic damage to enemy units around you.
FROZEN MALET:Some people say that this item is stupid for zac but belive me it gives u alot of health andsmall amount of ad and cause of its passive it will help u at casing.

U allways start with W the UNSTABLE MATTER cause it gives damage based on max helth of enemy.second ability witch u will max is E the ELASTIC SLINGSHOT cause it helps u gank and chase.Will the u will max Q the STRETCHING STRIKE at the end.

PROS:
good at ganking
good at escaping
relly hard to kill
its relly hard to escape him
can use his passive to survive
CONS:
lof dmg
he uses his helth to cast abillity
doesnt do so much kills in team fights

U start with blue than u kill the wolfs,banshes and little golems then u GANK.u must farm a lot and gank from time to time.