This build is for a pure support soraka, you will not be farming minions or going for kills, early game the object is to keep you lane partner around 3/4 life. After you get your ult keep an eye on your entire teams health as your ult is a global heal, don't be afraid to pop your ulti if you see a member across the map getting low and being chased... they'll thank you for it believe me. as the game progresses make sure you have an eye on you're tank or melee fighters health, use infuse on your mages and carry's to make sure the damage keeps coming and to keep your own mana high enough so that you can sustain your team..a good healer can make team fights super easy and keep your fighters nice and fed.

Pros:
best heal in the game
can turn a losing battle into an ace
no need to worry about farming
can escape a gank fairly easily
with rylais and infuse has nice cc potential

Cons:
low damage output
fails in 1v1 fights
easily focused down in teamfights
can be difficult to decide who to heal

ok first you get your amp tome and a health pot, you wont be using your heal on yourself early so this is essential to keep your lane sustained. try to stay in lane as long as you can, i usually go finish my lucky pick around lvl 6, now stay in lane if you can until you can buy your boots outright and your kindlegem...this should be around when the major team fights start happening so go heal and suck up the assists once you can afford finish your Shurelai's and start building your soul shroud, by this point you should be getting pretty fat on your assists and boss creeps, so buy your abyssal scepter when you get a chance to head to town. Next is Rylai's, i suggest buying the belt first to keep the cost in check when you finish it, the reason behind this buy is simple...aoe slow in a team fight every so often cast your starfall and watch the other team cringe as they cant run away or give chase....finally (if the game lasts this long) sell off your kages pick and pick up a will of the ancients...stacked auras and cc ftw

as for alt items, you could get yourself an early rod of ages to up your heals endgame or sometimes i swap out my surelys for an aegis of the legion when the other team is ad heavy.
Other than that i wouldnt change much...however soraka is pretty versatile as champs go so experiment with what you think is best