Learning to master Katarina, but I really struggle with her build path. Magicpen seems to work the best all in all over flat ap.
Is deathcap necessary if I can oneshot an ad carry with only ~400ap?
would more pen help against tanks or would the pen only help when I have more ap? 
Appreciate any input
MLDzXnRRR1 votesLudens/ Abyssal > tier 2 boots > if the enemy is stacking MR, get Void, if not - Zhonya/Rabadon > luxury items (Rylais etc)
Nameless Voice1 votesBuy whatever you think is most useful in the present situation.
For poke/farming/catching up, you'll want Luden's. If you need to be able to survive strong enemies after jumping in, get Zhonya's. If you're having a hard time against another mage (or AP assassin), get Abyssal. In most cases, that utility is worth more than the raw damage.
Get deathcap if you need more raw damage, especially if the enemy have little magic resist. If they have a lot of MR, get void staff first.
HadesBlades1 votesI generally go abyssal first item (or ludens if I want to roam a lot) and then I generally lead into dcap after that. The ludends -> dcap is very powerful and helps you clear faster, and allows strong roaming power. But if you want, you can hold off until it being your 3rd or 4th item, because both abyssal, ludens, and void gives enough ap, and mr shred that you can still tear through squish champions. :D
(try hextech it works pretty well, and is getting buffed next patch :D )
Catastrop1 votes rush is really reliable against most AP champions, after that I go into 
and 
. From there it's 
, 
and whatever is best for the situation. Honestly, Deathcap isn't necessary for Katarina because of her resets. Items like 
, 
, 
and are usually what you want to top of your build.
Squidward Dab1 votesRush abyssal if you're against AP champs and zhonyas if you're against AD champs. After that you usually want to get sorc boots unless you feel you can purchase another large rod before getting the boots.
If your team is ahead of the enemy team by a lot, deathcap is the better way to go as raw ap is usually the better stat for katarina. The only times I would get items like Liandry's + Rylais before deathcap would be if the enemy team has a lot of mr on their team and I need some way to bypass the mr plus the slow from rylais is quite nice. After that you can just get a void staff.
So basically
-Little mr on enemy team = Raw AP
-More mr on enemy team = Mpen items for tankiness and cutting through the squishies and tanks.
I'll often replace the rylais with void staff + abyssal scepter against ap's unless I feel like pissing off the enemy team with the slows from rylais because who doesn't love being slowed down while facing kat's combo
Plus, glass Kata is more fun in my opinion then mpen Kata so I'm a bit biased towards glass Kata. By mid-late game, if you have enough money, get the ap elixir for the extra ap whenever possible. it's quite helpful in case you can't afford the ap items you need.
Hope this helps.
Also, am I the only one who likes to place the items in a certain order in the item slots based on the value of the item??? Ex. from slot 1-6: Deathcap, Zhonyas, Ludens, Rylais, Void Staff, Sorc Boots
