is it crazy to build a Zz'rot Portal on off-tanks?
Shyvana was my main season 3, but I stopped playing her because she wasn't in a good place for the longest time, and I just picked her back up. Unless I'm losing jungle/lane hard, I generally have been building two offensive items (Bork/TF/Devourer's) and 3 tank items. Even though Devourer's makes clearing both jungles fast as hell, no matter how much $$$ you make you still are pretty squishy once you're sitting on TF/Devourer's and boots.
As a tank, you generally want to be building as much resistances as possible for whoever's fed on the enemy team, so you can survive longest in a fight with them. As an off-tank with no defensive items 20 minutes into the game, when teamfights are starting, you want as much survivability as possible against mixed damage. So the first buy is easy - health. Warmog's is a great item right now imo, allowing you to rush tons of health and passively regenerate it in between jungle camps and fights. The Zz'rot portal, then, is the easiest way to build both MR and Armor at the same time, at a very efficient 60 of each in only one slot. Since you have both Armor/MR from one item, you can afford to build a Randuin's/Banshee's as applicable depending on what the enemy team is running, whereas if you dropped the ZZ'rot portal you'd be forced to build a Randuin's and Banshee's and then have to decide between more health/armor/MR.
If you add up the base stats and ignore the passives (which are probably better on Randuin's anyway) it seems like I'm wasting money, but Warmog's and the Zz'rot portal are both cheap and efficient and allow you to become a mixed tank fairly quickly.
Also, split pushing + baiting with the Zz'rot portal is fun as balls, and Point Runner (+movement speed near turrets, alive or dead) is a very underrated passive. You can even dive the inhib turrets without losing speed!