This build looks a little weird but if you check my profile, almost every game is 20+ wins. My summoner name and name here is the same.
This build really shines if kat gets middle. Kat is an amazingly soloer, however u need proper planning b/c so many people can shut you down. I get BB first to harass a little but basically to trim down minions to get to lvl 2 and 3. I simply throw BB at the enemy and shunpo to an ally minion to trim their hp. Then I start to shunpo and BB and finally at lvl 3 use exhaust and go for the gank.
Once I am level 6 I kill the middle champion for the 2nd or 3rd time and start going top/bot. pick whichever lane has their champions lower. Run in behind them and use DL, then use Shunpo/BB if they make it too far away.
My build looks weird but let me explain. When its 20 minutes in and your at 10-15 kills and 0 deaths they will focus you. Once you get rylai's, you need to get a warmog, this adds over 1300 hp. Now your at 20 stacks and a great amount of hp(3khp at lvl 12-14 is ALOT), however your ability power is roughly at 286. So your burst is a little lower but now a 2 person gank is not enough. I've gotten plenty of quadra/penta/legendary(6 kills sub 90 seconds) early and late game.
At all 6 items+flasks I sit at around 5900hp and 670 AP, and this is a combination that is deadly. You become a tank kat with amazing damage. If their team is stacking magic resist, switch the second warmogs with a void staff. The point of an early warmog is to keep mejai's at 20 stacks, thats 160Ap+15% CD reduction. Also makes ganking at a tower and not dying very easy.
The key thing is to farm champions, early game any champion is easy if u harass enough and plan accordingly.