I wanted to get an opinion from my fellow summoners. It seems that if I ever build a magic resist item, it is absolutely useless. If I go tank and build items that add to armor or health, I definitely see the difference when my opponent attacks me. However, if I build magic resistance against a mage, nothing changes: I'm still taking the same amount of damage.
Leti the Yeti2 votesseems but its not ;D
67chrome2 votesI wanted to get an opinion from my fellow summoners. It seems that if I ever build a magic resist item, it is absolutely useless.
They aren't.
You're probably concentrating to much on the fairly low numbers of MR items over what they're actually providing. Honestly it's pretty hard to get a good feel of how things feel in the game with all the variables involved. MR is obnoxiously oppressive to run up against as most magic-damage heavy champions though.
As for the actual numbers:
You need ~150 MR to double your Effective Hit Points against magic damage as a typical level 18 melee (52.5 base MR on just about all of them at 18). With 0 MR you'd only need 100 MR to halve incoming magic damage, but everyone starts with 30.
For QWER rotations - you typically need ~450 AP to pump out double the damage, and ~750 to double the damage of most ultimates. If you go with 450 AP:
450 AP (double) is countered by 150 MR (half). Or 1 MR = 3 AP. As such, the 55 MR of 
actually negates an impressive 165 AP (
only offers 152 with it's own AP and it's %AP bonus). Spirit Visage is also notably cheaper and offers HP, HP/5, and CDR in addition.
It's also worth noting that on a per-stat price basis, MR is cheaper than AP in a 1:1 comparison (Negation vs. Blasting), so you're only paying roughly 1/3rd the price on MR as an opponent is on AP.
Finally - base HP on champions is ~2000 in most cases. On extremely cases it can go from 1600 to 2400, but most champions are close enough to 2000 that 2000 is a solid spot for mental math.
A typical QWER rotation does ~1000 to ~1200 damage from bases alone, so to even hit 2000 (especially vs. the base 30 MR everyone starts with) you need ~450 AP at level 18 (or ~150 at level 6).
To halve the damage with HP alone, you need 2000 HP. Obviously extreemly difficult to get with 1 major item, but AP can only boost their power by 33% in one go with Deathcap.
Anyways - 2000 / 450 = 4.444, so you only need ~4.5 HP to block every point of AP an opponent grabs. Considering you get 9.5 HP in a Giant's Belt per 1 AP in a Blasting Wand, also a pretty solid cost-effective counter there.
For actual AP tactics:
Most AP champions have 3 key qualities to keep in mind in terms of counter-building their damage output.
For 1 - don't mess with any burst caster when you're at 20% HP and hope to survive. Very few items allow that power.
For 2 - a tank's job isn't to tank damage. You're job is to disrupt and be impossible to ignore, while occasionally making a game-winning play by blocking a projectile or 2 for an ally in the midst of a fight.
Catching harass in a pre-fight situation will simply cause all the defenses you purchased to evaporate and remove whatever advantage they could offer, transforming a tank into a squishy. So - dodge poke. When that doesn't work, HP/5 is the sustain stat for most champions reliant on big defense to work - which is a sustain stat all 3 of 
offer in solid chunks (Visage even amplifies all HP/5 by 20%).
For 3 - Locket's active is your best friend there, though it sounds like your problem is more getting focused down as a tank than it is your allies being focused instead.
Anyways - MR itemization offers some pretty solid power and is very cost-effective at countering magic damage, especially when paired with HP.
AtheosisX1 votesSeriously?
