Hi ;)
Its my first build here and at the start I want to sorry for my poor english, its not my native language, i do a lot mistakes so u can correct me in comments :)
I will shortly explain my (imo best) ap/lane build for Skarner.

Pros:

+ His E is good harass tool in early game
+ good selfheal
+ funny to play
+ epic voice :)
Cons:
-squishy
-CC'ed easily

For runes I have chosen my old runepage with some M pen and m resist ;)
works good but u can improve that in your way ;)

Masteries are simple too:
9/0/21 for more magic penetration ,CDR and improve Exhaust spell
I treat him like every caster, so 21 in utility is must ;)

And this is time to think a little more
I had some problems with election of good items, i hope u will like my way of building him.

Early:
I start with mana crystaland someHP, this allow me to spam Q/E skill and stay on lane realy long. I B'ing when i reach 900-1k gold , and i spend it on Sheen(and ward if needed)
Next we will need boots - im using only(if enemy team is heavy CC) or.

Mid:
We should start building- Its core item which give us most of our AP.

Next Should beAnd now we can do some serious DMG.

W + autoatack + E + Autoatack + Q + autoatack sequence will be pain in the *** for every enemy ;)

Rest of the items should depends on enemy - if u need some defense build upor
For good DMG boost u will needIts great item with usefulll for u spellvamp and lifesteal :)

Only usefull are:
- U will need it becouse of lack of escape mechanism.
- great for chasing or escape, i found it usefull for easly hitting enemy with Skarner ulti.
- good for finishing enemies.

Skarner is good jungler, However if u like jungling this build isnt for You :)