This is a personal set of builds for testing purposes, though much of it are not creations or ideas of my own.

Items:

-Against enemy defenses:
Youmuu's: assassination potential.
Last whisper: against heavy armor.
Black cleaver: if your team have lots of auto attackers.
Blade of the ruined king: anti hp.

-Magic resist:
Malmortius: for extra AD.
Banshee's: better in skirmish situations.