I main jungle & Skarner is my most played champ. I have close to a 1000 ranked Skarner games at a 58% win ratio.

This build is different from most High Elo Skarner builds/guides. I don't know if this build is viable at high elo. But at around 1400 elo and lower, this build works. I like playing Junglers that can carry, while also being tanky & disruptive. There are 2 ways to play a tank/tanky bruiser. You can either go full Tank, and hope your built-in kit gives you enough peel to protect your carries. However, if the enemy team is smart, and you're full tank, they will just ignore you, cos you're not a priority target, let alone a huge threat. The other way is to be enough of a threat that the enemy team ignores you at their own peril, so they cannot afford to ignore you & go for your carries, all the while dealing with your peel & disruption. Esp. at mid or low elo, this is a good path to follow, as you cannot always count on your carries to be farmed or fed enough or to have the right items.

The recent nerf to Skarner's W, his shield hits him really hard. To compensate, you want to get early CDR, which helps esp. if you can get an enemy blue or two. Rushing Glacial Shroud is a good solution.

Start Regrowth + Pots for solo q, where you don't know your jungle will be protected or even helped against invasion. Bts + 3 is preferred start, but too risky for solo q. There will be games when the enemy team will invade your blue & your team is not there to help. Regrowth can get you a fast Philo Stone so you don't get gimped too much.

Last item is situational. Good alternatives are Wit's End, Atma's.. Sometimes, might just need to get a Negatron Cloak instead of Null Mantle & finish your Last Whisper, if u need more MR.

Lastly, try to focus on ganking & ward ward ward.