@Barkhwhip, thanks so much for the feedback!
As for your question about roaming, roaming is all about seeing opportunities to make plays in other lanes. If you see the enemy bottom lane overextended or low health, push your lane and head down there as soon as possible. I think your issue is that you might be trying to force ganks rather than waiting for opportunities to present themselves. Roaming is very risky because you sacrifice losing gold and exp in your own lane as well as risking a counter gank, so only roam when you know the time is right.
It's pretty hard to explain what I mean but I'm positive you'll begin to understand it soon enough. Thanks again for the feedback :).

Great guide overall!
You did put much effort into it, that's more than noticable.
You got my thumb up for sure.

As you said Katarina is a fantastic champ for roaming and ganking.
When encountering her in a match, I can just say that you are right.
But as I'm pretty new to the game, my ganks are always failing when playing her myself. I can't explain, but after obtaining Sorcerer's Shoes and Haunting Guise my damage is not even close to be enough for a strong gank. I assume that this is simply my own fault, because of missing experience, but can you or someone out of the community give some tipps on ganking with her to a newbie?

Any help is highly appreciated!

PS: Sorry for my bad english. I hope you did understand what I was trying to tell^^

@Tommeh, thanks for commenting. I'd love to shed some light and my own personal opinion on this topic. I know what article you're referencing, as I have read it before, and I will link it at the end of my comment just to make sure we're on the right page. Deathcap's passive has been increased to +30% multiplier instead of +25% since that article was written. Also, the author assumes Sorc Shoes and standard runes and masteries (22.8 + 8% mpen). With Sorcerer's Shoes, Haunting Guise, and the runes and masteries I use, you will have 37.8 flat magic penetration (15 from boots, 15 from guise, 7.8 from runes), as well as +8% magic penetration which is applied before flat penetration. I don't know the exact numbers behind all of this, but penetration is factored in before the damage is dealt, with % penetration coming before flat, so the enemy will essentially need more than 80 MR for Void Staff to out-dps Deathcap. High priority targets, such as the enemy AD Carry or mid laner, probably won't be building much MR at all (they usually have 42 MR on average). If you start seeing Negatron Cloaks and Runic Bulwarks, that's when you should get a Void Staff. I hope that makes sense.

As for "sorcs -> haunting -> rabadons -> ga build order," that's usually what I do if I'm extremely snowballed and want to end the game as quickly as possible. Typically if you're about even with your enemies, you don't want to rush a GA until later on in the game because you won't do enough damage to be useful.

Here's the article, it's probably the same one you were talking about
:
http://www.reignofgaming.net/blogs/a-different-view/diff-the-ender/23109-damage-analysis-rabadons-deathcap-vs-void-staff

@Tommeh I don't think GA would help at that point of the game as much as zhonya's would.

sinisteel i know you feel that this is preference, but mathimatically in every single senario, void gives more dmg than deathcap past 80mr, i dont remember where i found it, but you can easily just search for it on reignofgaming.net so, you should never ever skip voidstaff and absolutely shouldnt be a 3rd item. anywho how do you feel about a sorcs -> haunting -> rabadons -> ga build order? it seems fun

I see your point about cost efficiency and her main damage; and I also have found that I often keep the Lich Bane unprocced.
But I did notice that sometimes my combo doesn't oneshot a carry, and an extra Lich Bane proc did the job. It also helps with pushing turrets, considering the cooldown on your Sinister Steel.
Thanks for answering!

@TeaIsExplosive, I don't think Lich Bane is very efficient on Katarina. Yes you would be able to proc is extremely often with W, and Shunpo does automatically use a basic attack after its cast, but that's 500 gold you've put into mana that you won't be using. I'm all about cost efficiency, especially on Katarina. It could potentially work, but I personally wouldn't build it.

Also, most of Katarina's damage in team fights comes from her skill rotations and resets. It doesn't seem like a bad idea, I just don't like wasting stats.

What do you think about Lich Bane? Kat is automatically ordered an autoattack after Shunpo, so that increases it's AP ratio by 75%. It also gives 5% movementspeed.

@Theguidersguy, I find myself skipping Void Staff in most of my games. If it gets really late game, however, consider selling something for it. If there's 3 or more people with an item that builds out of Negatron Cloak or there's a Bulwark + Null-Magic Mantles, you probably should prioritize magic penetration. Sorry for the late response by the way.

Is it fine to skip void staff if only 2 people have mr ?