My first time playing Kat,I had no idea how to play with her so I sucked hard. But with time I got used to her and with my own build (this one) I became much, much better. Oh, I know my build isnt the best, but I advise you, after the patch they've done with Kat, never do Bloodthirsthers/AD Kat. It sucks really. First off you dont have Rylai, which is like a core item for her, rylai's slow will make you land your ultimate and make your enemies slow enough to catch them; it's HP. Its really important for kat to not be squishy. And Finally, AP Kat increases all of her skills (Bouncing Blades, Shunpo and Ulti) while AD only BB and Ulti... (YOUR SHUNPO IS FUNDAMENTAL!). Oh by the way, if the enemy team has really hard CC (alots of silences and stuns) buy a banshee's veil right after rabadon's.

Ok, Thats my runes that I use for kat, although I haven't decided what seals to use (CD or HP). But its basically that. Flat 15 AP in Quintensses, and Magic penetration, and CD Glyphs (oh Kat/Garen enjoy these).

I go 9/21/0 so I deal the most damage possible with Archaic Knowledge and be able to "tank" some damage with defense masteries.

First off, Doran's Shield. Of course. Item of choice. Your too squishy too use any other item. Since you dont use mana, you dont need doran's for nothing, and this shield will help your survivability. Sorceress Shoes. Why? Magic Penetration so you can kill everyone :). No need for Ionian boots cuz you are should have Glyphs and Seals with CD reduction. Rush into Rylai. Your Core item. Start off by buying a blasting wand. This will give you enough power for your early game. Then depends on you - giant's belt of amplifying tome. I dont care. After done rylai, you should be killing alot more because enemies wont run from you. Go for needlessly large rod and then rabadons. Now your ulti and shunpo will hurt believe me. Just keep farming and do follow the build. If there is too much CC buy now banshee's (you should be being its core items until now). If there is casters, it doesnt hurt to buy some abyssal scepter. Or too much physical damage hourglass. Oh its up to you. OH before i forget. Hextech is one of the must. atleast revolver. Spellvamp will make you handle much more damage since you will regen part of it.

Meh, skill sequence will be Ulti>Shunpo>Blades>Killer Instincts

(dont forget to use KI before shunpo'ing into someone).

Shunpo will be your nuke and killing skill. Btw, when you finish killing someone you can shunpo right away, cuz your passive will renew the cooldown of it, so keep that in mind when tower diving.

I chose exhaust because its a must. In early levels it will be your 1 person Rylai to ensure your kill. Then it will help you 1v1.

Hmm ignite without AP mastery for ignite.Why? I rather have 5% defense than having 10 AP. (This AP will be meaningless late/mid game and 5% defense can save your ***).

Wtf should I say here?

Well Kat is a great champion, her ulti is awesome, but never an initiator. Leave that to a tank like amumu or something. You come up next using your combo : KI > Shunpo > Ulti > Bouncing blades > shunpo (etc)

Pros:

Can deal large amounts of damage to a good amount of opponents (thanks to ulti)
Has big boobiez (lol)
One of the few Manaless/Energy less chars, So Cooldowns is what matters.
Shunpo is one of the coolest escape tools.
Very fun to play.

Cons:

Heavily CCed and she's done. Not even with banshees.
Sometimes can fail hard.
Needs some practice to be good with her.

Already said, you shunpo into the teamfight after like Amumu does his ulti. (use the combo, everytime!)

Good allies to have in lane:

Amumu
Rammus
Pantheon
Singed

(mostly anyone with a good immobilizer so you can do your ulti and they get all of your blades)

Worse enemies:

Amumu
Rammus
Pantheon

(same above, your best friends are your worse enemies.)