Skarner doesn't really have mana problems. If you get a philo stone, that pretty much is all the mana regen you need for the whole game. I play jungle skarner a lot, and I am often giving away my second blue buff because it just isn't necessary. A few good tips are, if the jungle camp is always dead auto attack are pretty ok to use. Don't do a w q combo for 3 bruised wraiths. If you have three points in expanded mind, that helps a lot too. Also, don't put a point in e pretty much ever. Its a mana dump and isn't worth it for fairly ****ty dps. Go q and w all day, and b happy. Skarner is a pretty spam happy champion. Just know when the spam is worth it and when it isn't.
The rest of your build looks fine. I prefer ninja tabia on skarner because they boots are cheaper, and it makes ganks a lot more likely to go in my favor. Merc treds are necessary because when you build warmogs, high health is a great soft counter to magic burst damage. I also like to build sheild of ageis before warmogs, because it helps your team out in the team fight, and it puts your MR and armor at about the magic 100 mark, which is good defense and wonderfully cost effective.