Soraka is not only a great support, but an extremely good Hybrid bottom lane Carry!
I've used this build four times, and won all of them, getting +10 kills and 100 000 damage dealt in ALL games. This is very underestimated, but actually will deal massive amounts of damage and piss the enemy team off a lot.

Pros:

-Very Fun
-Easy to farm with starcall.
-Easy to push.
-If playing against low levels, often will not get focused.
-Pisses the enemy team off.

Cons:

-Not meant to be a carry.
-Will not work in ranked games. (Most of the time)
-Very squishy.
-Not meant to be a carry.

Soraka won't do that much damage until you get yourIMO. You should be getting about 1-2 deaths, and 2-6 kills in the laning phase, average. By the time you get your and around the time you get your the game should be over. If not, farm up for your and be sure to carry your team! is VERY strong on soraka, as spamming the starcall which is pretty much a one second cooldown, will boost your AP up a lot, and with the good attack speed, you can get some hits in too.

Being a carry doesn't always mean an AD carry, Soraka is perfect! When laning, I like laning with; Alistar, Sona, Taric, Blitzcrank, or Vayne to accompany me. All of them have some sort of immobilization and will give you lots of time to get into position and starcall. If you and your partner both have heals, the other duo might dive you, and you can f**k them over with your double heals, and easily get the first blood/double kill.

Heal, well, most of time the other duo will try to dive you, or go for you early, so pop that heal and starcall, when they try to run, follow them with ghost and keep starcalling.

You have to rely on your team quite a bit. If you cant end the game in under 35 minutes, you're in some trouble, because even if you're 10-0 you still wont be able to carry if the game drags on this long. Make sure there's someone on your team that easily take your role and carry the team. USUALLY you will win in under 35 minutes, but y'know, just in case. Vayne is a good choice, and your AP mid as well.

I'm not joking around or anything, Carry Soraka is actually very strong IMO, and underestimated. People will often let you spam your starcall early in the game as they target who they think will do the most damage. Try it out with a partner in a normal game. Lots of other "Carry Soraka" guides always have a bloodthirsters, infinities edge, and like phantom dancers. Really though, the items you want are up there. Trust me. ;] Have a nice day.