this is my first build ever and i think sion is great ap because he`s shield is awesome. but i think they should give him more mana early game because cryptic gaze cost 100 mana all the time and he only have 200 mana LV.1 so if u use it 2 times youre out of mana thats why i think its important that u have mana regein masteries and mana runes. in this build ill describe summoner spells and skills and items and pros/cons and champs u dont wanna face in lane.

1.flash is my main summoner spell i always use it
2.ignite i think ignite is important if an enemy tries to run away with low hp u can ignte him and if someone tries to regein hp u can ignite him because ignite reduces their hp regein with 50%
3.ghost is good to chase or run away i think it works god with sion
4.exhaust is also good when gonna chase enemies also when youre going 1vs1 because exhaust reduces their attack damage and ability damage.
5.clarity is kinda good if youre solo laning and need mana .
6.teleport is always good if need to get to lane fast to save a turret or to kill someone .
7.heal works but i wouldnt recommend it .
8.smite u can jungle with sion but i wouldnt recommend it.
9.clairvoyance is not a good summoner spell for sionrvo.
10.cleanse is not good with soin
11.fortify is not good with sion.
12.revive is a noob summoner spell.
13.rally is the worst spell u can have with sion.

i think its important that u max the shield first because when u play ap sion the shield takes a big almount of damage because it scales on 100% ability power. i dont think its so important that u max enrage because when u go ap u are gonna relay on cryptic gaze and death´s caress
but remember to start the shield before u walk in to a battle because it needs to load before it explodes and remeber to last hit with enrage because u get extra max hp when u kill an enemy with enrage. the ulti cannibalism got a long duration but its best if u use it in big teamfights because u heal surrounding allies when u attack.

i think its important to have early game mana regein so doran`s ring is a good starting item then u have to start to build on your rod of ages. i think its iportant that u have rod early in the game. for boots i think if u gonna play offensive u have to get sorcerers shoes. morrelo`s evil tome is good for your ulti u get the cooldown reduction and mana regein lch bane is good because u get movement speed and sheen. then u need to go for rabadon to max out your ap and abyssal scepter is always god because u get magic resist and u reduce surrounding enemies magic resist it works like a surrounding magic penetration for everyone deathfire grasp is optional but it works

remember to last hit with enrage because when u do that u get increased max health but every hit u lose