Predecessor Builds > Drongo > Crit/Pen

Gives decent flat pen and good % pen. Hits super hard because of the crit and gives you some attack speed from viper to help bring up the overall dps. Ashbringer can be subbed out for anything you need really.
Ashbringer for more ability haste and attack speed.
Sky splitter for % health damage and attack speed.
Tainted rounds for antiheal and attack speed.
Terminus or kingsbane for sustain.
Breach for even more pen.
Demon edge to push your damage over the top and add a little extra sustain.