This is the "Tank" build I go for Nassus. Playing with this build makes Nassus virtually unkillable endgame. I've taken on multiple opponents at the same time and won. Farming his Siphoning Strike makes him a very hard hitter end game, especially when coupled with the 150% bonus from the Trinity Force. The durability provided by a primarily tank build enables Nassus to stand amongst the enemies and dump their health with his ultimate (5%health per second) and crush anyone with Siphoning Strike's tiny cooldown.

Pros
-Very Durable
-High damage output late game
-Points in Wither makes for easy ganks
-Quick movement speed to chase down kills

Cons
-Relies on last hitting for kills early game
-Easily harassed
-Little evasive potential