Hey guys.
Josh here, first build so go easy :)
Anyways, i'm a bit of a jungler and I'm a huge fan of Skarner. Skarner is a versatile champ who offers great ganks, efficient jungle clearing, AND A RAGE ENDUCING ULTI :D
Early game he is still a great champ, with the ability to rip some *******s early on.

Skarner is a champ that values many different combinations of runes. Of course the one I recommend most for survivability & clearing the jungle quickly is the set shown. If you want more sustainability, or less dependance on blue buff you can switch out your Greater Glyph of Scaling Magic Resist for Greater Glyph of Mana. This mana boost should be enough to keep you going until you're able to get mana items.
As for marks, Greater Mark of Attack Speed is the way to go. With this build, it makes up for the loss of not having as much AttSp. items, and also gets the maximum benefit from that dirty little phage you want to buy oh-so-bad.
Ssseeeaalllss. I always think of seals as a bit of whatever on Skarner. I just stick with flat armour for the seals.
Aaaand Quintessences. Again, just like the Greater Mark of Attack Speed I always like that extra amount of AttSp. to get dem Q's going. One of Skarner's great pro's is that he is amazing at clearing the jungle with a good amount of attsp. and mana.

As per lots of junglers, smite is an essential spell.

Must Have

Smite

Advised

Flash
Exhaust
Ghost

Flash is a great initiation or getaway spell, as you can flash into a fight, grab their ADC and pull 'em out of there.
Exhaust, a real 'slaya'. Once you have an item such as phage, exhaust isn't as useful, but is still handy-dandy for those slippery gypsies.
Ghost is a sort of different flash, as it last over a longer period of time, and also gives great chasing abilities.

Not so good

Ignite
Heal
Teleport
Cleanse
Surge

A Big No-No

Clarity
Promote
Clairvoyance
Revive