Hello! i've seen many Sions that not capitalize the ultimate, and many that are based in his ultimate. Well, with that build i propose a Sion very effective with his 4 skills.

About the summoner skills, i choose Exhaust cause this skill give a lot of survability to the champion and allows him to catch his victims when they try to escape, also is very useful against melee characters, and Clarity cause Sion have a considerable problem of mana in early game.

Items and Play: we start with Rod of ages to accumulate life, mana, and ability power. that and sorcerer's shoes will bring us a effective early game; we can start to kill with a burst partner in the lane like akali or ryze. simply go to fight with the shield on and stun in the right moment to unleash all the damage and allow your teammate to do the same without danger.
after that, i buy Lich Bane and Nashor's Tooth to become in a realy strong Sion in all aspects. Rabadon's Deathcap is a mega power up to your q and w, and Gunblade complete your ultimate and you. (and gives you another slow skill)
We'll deal huge damage with stun and shield, have a good survability (we'll arent made of paper), and especially we'll have that loved godlike sensation with the ultimate on hehe.

¡¡GL & HF!!