~WARNING, THIS GUIDE IS STILL IN THE WORKS~

If you have any feedback, leave it in the comments, this is a fairly new design I'm fiddling with, and still haven't finished it entirely so bare with me.

Start by getting a smiteless blue, and start with Shattered Earth for a faster clear. After you grab blue, rush to red and use smite to kill it. If you can, gank top, it will most likely not net you a kill, but will give your top lane an advantage. After that, get wraiths and wolves. Then check to see if you can steal wraiths and head bot for a gank. After that you should back and buy.

I'm still working on this, but I've got the basics down, I was going with Tear of the Goddess for mana, but found I needed some health late game so I swapped it out with a Rod of Ages.
The only three items I think are a must on AP skarner are Nashor's Tooth, Rod of Ages, and lichbane.

If they are a really heavy AD team, swap out Rabadon's Deathcap for a Zhonya's Hourglass.

If you are getting bursted by a mage, swap out Spirit of the Spectral Wraith for Spirit Visage because it will give you increased CDR aswell as more healing from Ixtal's Impact.

When you come in to gank, you want to fight near minions, unlike other junglers because of Ixtal's Impact. I've come in and ganked someone when there were two waves, and was healed nearly half my health from Ixtal's Impact.

When you come in to gank, you want to position yourself behind the enemy by leading with Seismic Bastion, land a Shattered Earth and lead their flash/jump(depending on the champ), after that use Ixtal's Impact and quickly use Impale. Drag them back while using Shattered Earth. If you find that the lane you gank for misses a skillshot when you drag them, hold them in place with Impale instead of dragging them.

This Skarner build is played a little like a melee assassin, because of Ixtal's Impact and Seismic Bastion you can take a lot more abuse, but you're still not the teams tank. Your job is to try to position yourself to either catch someone out, or use Ixtal's Impact and wait to grab their carry with Impale. At full build your Impale will deal nearly 1,000 damage after magic resist against their carry, along with Ixtal's Impact and Shattered Earth you should be able to kill their carry in a single combo.