Runes:

• Greater Mark of Scaling Ability Power sucks. It will not deal more damage than Greater Mark of Magic Penetration.
• Greater Seal of Scaling Armor is not needed. You'll need Greater Seal of Armor to absorb early game basic attacks, or else you'll take a lot of poke trying to farm just from basic attacks. We don't want that do we?

Masteries:

• You don't need Brute Force to reach the top, what you could take is Double-Edged Sword , Butcher and Feast .
• The two wasted points in the defense tree should be removed from Enchanted Armor into Unyielding and another mastery in the third tier of your choice.

Items:

• Sorcerer's Shoes - Furor - Wut? Please don't.
• Quoted:

  Katarina is a High burst Ap Assassin
  
  If you want her to burst, remove Hextech Revolver and add Deathfire Grasp.
• Boots start isn't good.

Skill Sequence:

• Max Shunpo over Sinister Steel?

Improve This:
Make a final build thing for ur items, WHY SCALING RUNES??, no AD runes, no AD masteries, take full AP wich u did clearly not do now, as Arcane Blade is not taken. You have a lot to change, my friend...

You runes, masteries and items are wrong. Only thing you got right was your summoner spells. Will explain why when I get back home though. Be patient ^_^