Welcome to my first Skarner build. :)
Thats why i choose Skarner ,because i like jungling/tanky champions :D
If you bought it but you can't really use it than try out my build .. i think it will work.:P

First you have to buy a cloth armor and 5 health potions .Go to the blue and ask a team mate to help you kill the blue (You can use a health potion). After Blue you are lvl 2.Go to the wolfs and kill them then go to the wraths (you can ignite the big one) use a potion . Now you must be on lvl 3.Go to the Golems it gives you a lot xp (use health potion).If you have 700 gold than go back and buy a medred blood razor.. If you don't have that mutch gold go to the wolfs when they spawn again and to creeps .Now you have that mutch gold so buy it.Now go to the Red and kill him .You got the buff and you are lvl 5 (i think).Now you are free you can assist on the lanes or you can lvl up to lvl 6 in the turrets.

Recommended items at mid of the game:
Warmog!
Force of nature.
Mercury's Treads
Sheen/Trinity Force

Not so important but you can choose it:
Frozen Mallet
Rod of Ages
Rylai's Crystal Scepter

yeah and by the mid of the game when you have warmog's armor and thorn mail you can sell wriggle's latern..

Skarner dosen't do mutch demage without Sheen so its important to buy it.
At early of the game after reaching lvl 6 you have to assist on the lane by ganking.
You can slow enemys with your Crystal Slash and hit him and follow them to pick up the kill.
If on top is for example 2 enemys than hide in the bushes and slow them with Crystal Slash and ask you team mates to assist by killing an enemy.It is important to help the lanes!!

Pros:
Very good at ganking.
Strong ulty.
Many CCs.
Tanky and do lots of demage.
Low CDs.

Cons:
Easy to gank.
Weak early the game.
Junglin is requed.
Important to buy a Sheen.

Thats why i choose these runes because im an ad player i play champions like Tryndamere,Twich,Shyvana,Teemo,... Skarner don't really need health or armor or magic ressistance .. You can get these from the stuffs you buy.

You can choose it:
Well yes it is a jungling build so you need Smite!!!
Ghost: Ghost is pretty good by chasing enemys and slow them with your crystal slash.
Ignite:It is good too when your enemy got low hp and trys to run away.
Flash: I would say that flash is perfect!Because when you are under attack or slowed and they try to kill you, You can flash away and run to your turret or to your team mates.

I don't think other summoner spells would be good ...

I choose my masteries so that i do lots of demage but still im tanky.

Thanks for reading my first build.
Sry for my bad english i learned from school.

Please leave comments!