Hey guys!
My name is Josh, or Accipitrade, and I'm gonna show you probably one of the most OP Sion builds I've seen or played with. This is my first build, however, so please bear with me if some of the stuff is off. I'm always open to suggestions and ideas, so don't hesitate to let me know if you think something should change!

Pros:
-Never Dies
-Has tons of CC
-Extremely useful in team fights
-Isn't straight-up tank, has some damage too
Cons:
-Mana-hungry early game
-Can't 2v1
-Relies on team for solid damage output
-He died and noone let him R.I.P. It's the apocalypse!!!

So before we get any further, I'll explain essentially what type of build this is. It's a team fight build, meaning that if you're in Solo Queue, or some other place where everyone is toxic and never communicates with each other, you literally have no chance at helping to carry.

Some people max their Q first, others their W, others their E. (I really hope you don't try maxing your ult first, cause it won't work ;) )

I max my E first, and my Q second, because Sion, in my opinion, really relies on his laning phase.

When you max your E, you can out-sustain almost any top laner. You don't even have to let them get in melee range, just pop your E and you can chunk them pretty nicely. Your Q is second just in case they get pissed off cause you E'd them, so clunk'em over the head with your trusty axe and that should send them running.

Your W is last because it won't really be useful to you late game, which is why you max it last.

Since you brought smite, you might as well jungle some too!
To start, let's get one thing straight:
You're playing Sion. If you don't steal camps, it's kind-of rude to the enemy team.
You wouldn't invite a guest over and not feed them, right? Same principle.
Here's a great example of a red buff being stolen, thanks to Vefy: Play Video
Keep in mind this can be done at full health as well, that way it doesn't alert the enemy and you can pretend you're a ninja zombie.

You can also steal wolves, if the enemy jungler is going for red first.
It's essentially the same thing as stealing red.

**START W, SO THAT YOU GET A FEW STACKS ON YOUR PASSIVE EARLY**

In addition to pissing off the enemy top laner, you can piss off the enemy jungler too! isn't that great?

Take krugs (yours, or theirs. not really important.) religously, as they're in your lane and hey, the more stacks on your W, the better.

Gromp is really the best camp to take, as you don't have insane burst capabilities, this helps with a couple of nasty ticks of poison damage.

Feel free to use your smite to take wolves, especially the enemy's, and generally while clearing so that you can get whatever you're after faster.

Keep in mind, always ask your jungler before taking his camps. After all, you have an entire lane and he only has the jungle. Be nice.

Thanks for reading, and I hope you liked the build!
Please, don't forget to vote and drop a comment on stuff that I should change, add, clarify, or just plain old Questions, Compliments or Concerns!
Josh :D