oopen up with a doran's ring and try two lane with someone that can deal tons of dmg fast(examples: master yi,nocturne,etc) go back to yor base area thing if you didnt already and start working on your boots of lucidity(it will allow to spam ur stuns out and sheilds making it VERY difficult to kill you) if your confident in your sion skills instead of will of the ancients you could get mejai's soulstealer(also gives extra cooldown which is nice but be careful if you get this item because you gain stacks by gaining kills and assist but you lose some if you die)buy a saphire crystal for extra mana and buy catalyst protector and build it into a banshee veil or rod of ages(if your taking all the enmy team's disables get a banshee veil) save up for your rabadon's deathcap(try to get the needlessly large rod first if you can) same rule appies to zhonya's hourglass sell your dorans ring and buy a tear of the godess(you can buy this first but i tend to like doran's ring as a better starting item) upgrade tear of godess to archangel staff
hope you enjoy playing this epic ap sion and may see you on the feilds of justice on day

start with brawler's gloves(buy hp pots or mana pots doesnt really matter in my opinion)upgrade to avaric blade and keep it thereuntil after you get your madred's bloodrazor after you finsh your avaric blade buy mercury treads or berserker greaves(depending on enemy team lots of cc merc treads) buy vampric scepter or if you can just buy excution's calling all at once it makes your e(enrage) have almost 0 effect on you(it cost hp thats what i meant to say) start buying parts of infity edge makes your crits just destimate enemys when you crit(order doesnt matter) grab yourself a madred's razor and buy madred's bloodrazor upgrade your avaric blade(which by now you probably had for 15-20 minutes) to youmu's ghostblade after that buy a phatnom dancer makes you wayyyy faster and the extra crit chance is awesome cause of your naturally high ad(hes getting nerfed i believe =() an alternative trinity force(for phantom dancer so dont ask what the alternaive is for)

sion can play almost any role your team needs whether it be ap,ad or tank(yes sion can tank) once you get your enrage skill try to last hit as often as you can because you gain bonus hp whenever you kill a unti before you get your enrage skill dont worry as much about last hitting(which is way easier to do with a ad sion)

cons:
squishy early game
vulerable to gank
pros:
can fill any role needed
can tank turret if has enough ap on your sheild
can 2 hit a casssiopedia

for ad sion i tend to personally take exhaust and ignite exhaust is one of my all time summoner spells for ad champion slows the enmy and if you have improved exhaust reduces their damage output by something percent and item damage(not sure what the stupid percent is i'll have to find out later) ignite i like cause sion isnt 1 of the fastest heros and then ur like ugh he only had 10 hp left ignite would fix that problem alternatives for those two spells are
teleport
flash
rally
heal
(never ever use revieve its a spell for trolling plus you shouldnt be dieing)

sion can jungle and a lot of people underestimate him as a jungler
i personally just can't i ever you the right skill order which is why i dint give a build for jungle sion but jungle sion usually goes ad/attack speed sion can easily solo the dragon after level 6 (i did it with a laning ad sion w/o smite so it is indeed possible)
don't have much more to say bout jungle sion if i played jungle sion sucesfully i could go more in depth