Katarina is still super strong even though Riot nerfed her stats and nerfed Warmog's and other items that are core on Kat.
You'll want Rylai's 100% of the time. It's the only health item Riot didn't nerf with the recent patch. Sorc shoes and Haunting guise are both amazing on Kat due to her base values. You'll want Sunfire like 99% of the time unless the enemy team has no physical damage.
This build focuses on surviving fights, getting resets, and overall just being more utility/tank based instead of a full DPS build. Don't get me wrong, your damage is still insane with this build.