im not sure how to make one of these because no one ever looks at mine or even cares....
well its worth a shot. so this is MY personal build which i use myself and actually do really well with. The extra durability early game allows me to farm easier as well as prevent myself from dieng as much late game. I pick up a hextech for the early damage and spell vamp and then move into sorc boots for the magic pen. Rylai's is my next choice for its hp damage and slow (which is greatly beneficial on kat). Will of the ancients is my next choice of item because of the sheer amount of bonus ap and spell vamp. People debate on hextech gunblade but i say go with what you see fits you. I get rabadon's for the obvious damage increase and rush a zhonia's hourglass. This allows you to gain that extra bit of durability and has a great effect if chained with your ultimate. Katarina's ultimate is a channeling ability so if you use her ultimate and the effects of zhonia's hourglass immediately after while it is channeling, the ultimate will keep damaging while you are invulnerable. This is a great strategy to employ during the beginning of a team fight. Abyssal scepter gives that extra damage while giving durability to magic users and lowering the MR of your enemies while your bursting them at close range. now go play with my precious kitty kat and good luck~