Remember back in Season 5, when tank Ekko was reigning over the meta? Well ever since then he has been gutted from his tank role and was molded into a bonafide assassin. But what if we could bring him back? He of course won't be nearly as good as he was before, but he still packs a punch.

Advantages:

Great at securing kills and sticking to people with his E.
Decent at killing tanks because of his % damage on W.
AOE Stun that can single-handedly win teamfights.
Does decent damage despite being tanky.

Disadvantages:

Not too great in the late game.
Very reliant on cooldowns being up.
AOE stun has long wind up animation, not always reliable.

I have been trying to make hybrid tank Ekko work ever since he got nerfed, but due to his low health pool and there not being many AP and resistance items, he fell flat most of the time. However due to the new rune system, resolving giving you access to many health reserves, it greatly boosts his survivability in fights.

Resolve:

Grasp of the Undying: A must on tank Ekko, provides him with sustain and damage in the early game, and tons of HP in the late game. Easy to stack HP with his E.

Demolish: Great at picking off an early tower, together with Ekko's great waveclear with his Q. Also helps him seige int he later game.

Conditioning: I personally like this as it gives Ekko huge survivability in the late game (20+ MR and Armor usually), but you can change this as you see fit.

Overgrowth: Again, exchangeable. Second wind can also be useful in sustain in lane, however due to Ekko's all in nature in lane, I like the late game tankiness of overgrowth.

Precision:

Legend Alacrity: Another must have on tank Ekko, works well with both his passive and W passive.

Coup De Grace: Helps amplify Ekko's W passive damage, and finish off low health opponents.

Starting

Usually go corrupting potion because of the synergy between grasp. Doran's Shield is okay as well (normally get on first back though).

Core

Tank Ekko needs enough AP for his heal to do anything significant, so with that in mind, most of his core items need to have some AP behind them.

Rod of Ages: A must on tank Ekko, build ASAP. Provides him with sustain when spamming
abilities, tons of health for survivability and mana sustain (which is good since tank Ekko is a pretty mana heavy champ) along with a lot of AP.

Iceborn Gauntlet: Another must. Usually build after Rod of Ages. Provides him with even better chasing potential with CDR and slow on E.

Banshee's Veil: Pretty much the only viable AP + MR item on Ekko, spell shield is good too.

Zhonya's Hourglass: Again, pretty much the only viable AP + Armour item on Ekko, active and be used to stall for R and W.

Last Item Options

Pretty much any tank item that gives HP and/or Resistances.

While he might not be the greatest meta pick, he is still really fun to play whether it be in Normals or Ranked! I hope you enjoy the build and let me know if I should add anything else or answer any of your questions. Feel free to ask!