My summoner name is NaClBait and I'm a Sion main with 500k+ mastery points right now. These are some of the builds I've enjoyed running on Sion.

I personally enjoy Sion a lot, he's a fairly straightforward champion but not completely braindead. Learning how to set yourself up for a high-charge q or zone enemies off of your backline is really fun and landing a max range ult after drifting through the jungle always feels fantastic. Sion can function great as a tank but his absurd ad scaling and synergy with health scaling items such as Titanic and Sterak's means he can also spec into more damage-oriented builds while still being relatively tanky. The ability to switch up your playstyle on Sion and still be relevant keeps him from getting boring and is probably one of the main reasons I still play him.