Starting off with boots and 3 potions really helps you with your mobilty around the map, to gank or move from one jungle camp to the other. After recalling, buy gold per 5 items - Philosopher stone and Heart of Gold. The philosopher stone allows Skarner to spam his Q a lot and not lose much mana. This gives him a lot of sustain in the jungle because of the mana and health regen. Heart of gold gives him the tankiness he needs in early team fights. After that, you want to upgrade your boots to tier two boots such as boots of mobility. Buying boots of mobility allows skarner's ganks to be very strong and consistant. Purchasing boots of mobilty is very helpful as skarner needs to engage by running to the enemies and ulting them into your team. Following up with Aegis of the Legion and Shurleya's revelrie helps you and your team. Shurelya's is extremely good for skarner as he needs that movement speed boost to get to foe's and ulting them. Trinity force will give him a lot of damage as well as the tankiness and movement speed to engage team fights. Getting a frozen heart will increase your armor by a lot and will really make him a ''God Tank''. Finally, upgrading your heart of gold into a Randuin's Omen will prevent Attack Damage Carries from kiting you and it also gives you a lot of armor.