Hey guys, my name is Nick (ign Freelo Airlines) I play in EUNE and am currently Gold II.
This guide will be on Katarina, a champion I used to main back in S5 before the ranks came out so unfortunately, I did not get my rank 7 kata back then so I decided to do it now. I wanted to try something more unique than the normal build everyone is playing right now so I came up with this build and it's been working quite well for me in the Gold Tier.

x9 Armour seals can be replaced by Scaling Health

x9 APM marks can be replaced by Attack Damage

x9 Magic resist glyphs " " " by AP(not recommended)

x3 AP Quints Should always be AP Quints

Pros :

Hard to kill
Good AoE
Hextech synergy with AoE and Visage for great Healing
Acts as an off-tank so doesn't die as often late
Strong Teamfight Presence
Good Ganks

Cons

Vulnerable to CC
Weaker Ulti than standard fullap build
Weak pre-6
Vulnerable to ganks if E is down
Falls behind more easily if she can't get her items

Play more passive pre-6 and farm using abilities if you are getting your lane shoved.
At 6 start roaming if your laner if you see an easy gank or if your laner is mia or killed.
Leaving opponent in lane can set you behind if you fail the gank as you lose exp and gold.
Once you have your core. (hextech Rylais spirit) you can jump onto their ADC in teamfights and your ulti will do the rest. A common mistake new kata players make is wait for ulti to finish chanelling. That is unnessesary as after 1 or 2 kills you can use reset to jump to a fleeing target instead of getting that 200dmg on the nearest enemy(dealing 200 dmg with QEW is more efficient anyway)

This is my first league guide so sorry if it a bit sloppy and maybe lacking in some places.
I appreciate any constructive critisism and help with fixxing the build as Im new to it aswell.