A strong, expensive, and powerful item that serves as a significant power spike and allows them to scale into the mid-late game well.
Mages have 
Bruisers have 
AD Carries have 
When you build these items, you feel good. You feel you've achieved a big, meaningful power spike. Tank items are uninteresting, boring, and cheap.
I hope riot uses the upcoming pre-season to work on tank itemization.
Tanks also need items that bruisers/fighters/adcs wont take on the side.
I think that tank items are a lot more interesting than most other items in the game due to a ton of special abilities they have, that being said tanks are kinda lacking the big stat sticks other roles (except supports because who cares) have. There is also so many item counters to tanks that in late game you are kinda lucky if you live 8 seconds in a team fight because the enemy team has so much damage, armor pen, grievous wounds, magic pen, etc. That just negates your stuff. Small scale fights feel awesome but in team fights it's just like, why am I even here?
Step 1: Cut damage in half across the board. Step 2: ??? Step 3: Tanks are viable.
A tank has two jobs when they initiate.
1.)to survive 2.)to CC
The major items always give the tank health, defenses, and maybe even some CDR which help with exactly that.
A big strength to tanks is that they don't have a powerspike item that need to rush in lane. Do you know how fucking awful it feels when you're behind on someone like Darius, and you're still stuck building your core while your laner has two items on you?
Tanks don't need to get fucked harder.
the issue is, against the rest of the enemy team which usually is 4 squishies or 2 squishies and a bruiser and a tank sp or something, ap items ad items that powerspike are equally effective.
If you rush warmogs your not getting its passive, if you get an armor item you are weak vs ap and vice versa. its not balanced
Plating should be nerfed, so that tanks don't get snowballed on in lane, maybe even give tank items some adaptive force (just a tiny amount).
This way defensive options can create an effect of loss prevention, instead of an effect of "forfeiting all my plates to the enemy snowballing bruiser who can just walk up and take plates while I play the drums on his ass because I do no damage"
The only item that I found to be very good for tanks is 
and that's situational
It was supposed to be warmogs... but they fucked that one up when they didn’t want other champs using it.
They just need to make an item that has bonus hp /armor/mr based on how much you have... kinda like how ornns passive works.
Gives tanks big boost, stops abuse for squishy champs.
