This build is basically Sion taking advantage of items that give Health and utility. Items like cinderhulk and face of the mountain and righteous glory are what i mean. yes face of the mountain on a champ that isnt playing support. this means you can get further into your build earlier making this build take advantage of sions W which scales with health which also synergises with Face of the mountain and cinderhulk.
take smite as this is a jungle build revolving around cinderhulk
exhaust is necessary as ganking is very hard without it.

FOREWORD this build lacks in the damage department, this means you won't be dealing huge damage but you will be holding down the enemy so your ADC can do the damage for you. the good thing about this build is its ability to lockdown an enemy hypercarry. It doesn't matter if you have 999 kills and 0 deaths with 420 assists if you cant move because a sion is sitting on you.

Pros
+ very tanky
+ exhaust makes ganks easy
+ huge utility with items
+ good peel
+ overwhelming presence due to CC

Cons
- low damage
- low mobility (apart from your ult)
- becomes less scary late game
- relies mostly on the team to follow up

Your jungle path is simple. Gromp -> Ancient Golem(blue buff) -> Top side scuttle crab -> Wolves -> Brambleback(red buff) -> Gank bot or mid.

when Ganking bot prioritize the immobile lane partner, and use your exhaust to make for an easy E into Q+W at the same time, then use W again to finish off the target.
Be sure to communicate to your Botlane who you are targeting.

Midlane ganks are more dynamic, if it is a midlaner like Twisted fate or lux then move in to get between them and their tower. Use exhaust and E to slow them for an easy setup into Q+W but be warned midlaners commonly flash so aim your Q a little towards their tower so you can zone them away. However laners with escapes such as zed or katarina ar emuch harder and require you to either wait for them to use their escape aggressively or you can walk away.
Warning if the midlaner is LeBlanc don't bother ganking unless she is tower diving your laner, she will get away... i guarantee it.

Your ganks require your laner to do most of the damage, this build revolves around tanking and Controlling the enemy team for as long as possible. For sion a full combo of R->Q+W->E+Exhaust means the person you are targeting isn't going anywhere for quite a while.

After you've purchased your Face of the mountain don't be afraid to share your laner's farm (as long as you have stacks of course) you both get XP they get HP and you both get the gold. Win-Win.

Sion becomes overwhelming in the midgame mostly due to the items he has give him large amounts of health, so much that it is normally too much for an enemy to burst through. This means sion is basically a stunning wall of meat, see what i did there. Remember dragon is always an important objective you should be trying to take it whenever you can.

if the game progresses any longer than 35 minutes you start to become considerably less tanky, due to the lack of armour and magic resist. However do not be swayed to give up, this just means you now play as the utility role, you heal, peel, and steal(as much farm as you can with your targons). You become your ADC's best friend, all you have to do is stand next to them and bully any would-be assassins away by a) Yelling at them with E b) standing directly in their way using your W to persuade them c) threatening to crush them with your Q (if you choose this option make sure your ADC doesn't run away from you or d) my personal favourite, you just run at 'em with R preferably do this point blank straight into Q+W+Exhaust. don't forget to let go of Q as soon as they are free from the stun. Then even if they manage to get to your ADC use your face of the mountain to give them a free barrier.

when ganking a lane you may be frightened by the tower, do not be. Towers take a very long time to kill you, and as you are stacking health from cheap items you will outscale the tower's damage most of the time (apart from OP laser beam shoop-da-woop towers) using your W and face of the mountain can provide you a large shield to dive towers with.

stand in midlane at the second turret, Charge down the lane using R straight into an unsuspecting midlaner. Use Q+W straight after you hit.

while protecting your ADC it can be mentioned that charging point blank with R is quite effective as it ensures a hit and allows for your ADC to re-position while you CC the assailant.

using your W as soon as you use your R means you can potentially drive by and explode a low HP enemy that has dodged your charge, by detonating it when you get within range.

although this guide is very bare bones, it is still a work in progress and it is my first guide. any feedback is greatly appreciated.