Welcome to my first build guide on mobafire! :)
I have some difficulties in english but i will try to do my best!
I'm sorry if i make some mistakes...

In my opinion, Soraka has the best heal in league of legend ^^
The only problem is the cooldown of his heal, 20 seconds... but it's
quickly compensated by cooldown reduction items!

I played with her so many time (it's the first champion with which i played :3), and i tested many build, so i really spent time to developing this build.

I often take the same summoner spells:

Basic spells:
Teleport + Flash:
==> Teleport: to help another lane or arrive faster near the action =)
==> Flash: Soraka haven't escape spell so it's a necessary summoner spells if you want survive!

Pure Heal:

==>Flash + Heal

With this combo, you can save yourself and your team ^^

Other Choices:

==>Flash + Exhaust
==>Flash + Ignite

You can take Exhaust or ignite if you want. Particulary if your carry take Heal as summoner spell.
But i don't take Exhaust and Ignite because Soraka is really squishy is early and mid game...

Pro:
+best heal in the game
+ulti can save the team
+silence
+she can give mana to allies

cons:
-no escape
-low damage
-always focused xD
-squishy (exept end game)

I have helped many champions with Soraka, so here is my opinion of the best
team work Soraka + Carry:

Ezreal + Soraka:i really love this team: Soraka may be aggresive and it's very rare. ^^
It's really funny!

Anivia + Soraka: Anivia uses lot of mana, so soraka is really helpfull, she gives
mana regularly =)

Ashe + soraka: It's a great team to farm a lane i think.

I hope my guide helped you ^^

it's certainly not perfect and a little small for a guide and i'm sorry :'(

~This is my way of playing~
Everyone has his own way of playing a champion, the important thing is to have fun! =)

Good Game!
Sylfeanne