you got a pretty decent guide..+1

Runes:well for marks i would rather get greater mark of desolation but w/e..and for quints Greater Quintessence of Movement Speed can help skar alot when chasing and in jungle..and it seems that you want alot of movspd in this guide.

masteries: your masteries seem weird and arent focused on an aspect..a 9/21/0 page offers you more hp/armor/movspd/gold/cd that will help alot..you also wont miss any offensive masteries there

your build is decent item-wise but Mobility Boots are not good at all(maybe for Shaco or Twitch but not Skarner) as it dosent speed you up in battle..i'd rather get Ionian Boots of Lucidity so i can use exoskeleton shield more...and you early items are VERY expensive (over 6k)..so i think you should move Sunfire Aegis to midgame and get Sheen or Phage in earlygame (it will increase your dmg by alot) and Phage gives you health too..

thats all i got..gl with your guide