League of Legends XXXVIII: Featuring Mumble, The Giant Halibut

[ex cathedra]

Damage really isn't a primary or even a secondary concern on Skarner, and so while Triforce and Wit's End are nice they hardly ever take priority over Aegis, FH, or Shurelya's. Even then, they aren't always the best fifth and sixth items.

Edit
If you have *any* intention or expectation of ganking before the 4 or 5 minute mark, not only as Skarner but as almost every jungler in the game, you need to start boots. They're also the best starting item as far as clear time is concerned, so there's that.