This guide is for those wishing to play Soraka as an AP carry or solo top. While Soraka will still have nice heals built in, this build doesn't emphasize them. The play style of this Soraka will be mainly using starcall to harrass and farm early game, followed by a strong mid game, and contributing to end game teamfights by her ability to massively decrease an enemy's magic resistance.

I choose to go 9/0/21 on Soraka, but even for an offensive Soraka, a case could be made for 0/9/21. 21 in the utility tree is necessary, especially for the summoner spell cooldown it gives. I will always grab 'cripple' in the offensive tree as well to add even more mana shredding to my exhaust spell.

I start every build with a Doran's Ring. This gives you the best sustain in lane and can usually help me start out with 1 or 2 early kills. Most enemies will underestimate Soraka and be outmatched by her Starcall + Exhaust right off the bat.

When I have 800G, I head back for a Philosopher's Stone. This could be considered optional, and sometimes if I need the health I'll build it into a Shurelya's Reverie later. The reason I get this before boots though is that the gold per second makes a noticeable difference in how quick I can get my core items.

Next I go with Ionian Boots of Lucidity. Mercury's Treads are also an option if the tenacity buff they provide is needed, but the Ionian boots are the clear winner due to the 15% CDR they give. This always constant spamming of Starcall, which is your main source of damage.

I rush Rabadan's Deathcap at this point for the ability power. After getting this item, your Starcall will be doing some serious damage to the enemy.

Rylai's Crystal Sceptor is next because the 15% slow that it provides is invaluable for killing enemies that are trying to escape. It also gives Soraka a bit more survivability with 500 Health, and another 80 AP. A must have item on Soraka.

At this point, I build items situationally. After your core build, it's never a good idea to follow the exact same build every game, because you should always be reacting to what the other team is doing. If I need some magic resistance, I'll build a Banshee's Veil or a Frozen Heart. If I'm getting bruised I'll generally build Thornmail.

Another item that is very situational is Will of the Ancients. I will build this if I am laning with another caster for the ability power buff.

The first three levels I get Starcall, Infuse, then Astral Blessing. Early game I farm with starcall, replenish my mana with Infuse, and heal myself with Astral Blessing. After that, I prioritize Starcall and Infuse. Starcall is obviously most important, and Infuse does quite a bit of damage on the enemy, as well as keeping my mana full from spamming Starcall.

I have experimented and found Flash and Exhaust to work best. Flash helps Soraka get around the fact that she is a slow champion by allowing her to flash to chase or escape. For those situations where an enemy would have died with just one more Starcall, flash makes a huge difference.

Exhaust is the next best choice because it basically renders an enemy useless for 3.5 seconds. With a high CDR, that's a couple Starcalls and an Infuse, and almost always will net you a kill. How much damage can you do in 3.5 seconds? With this build, a lot. The -10 Magic Resistance it does also makes this valuable in team fights.

Ignite is a decent choice as well for Soraka. Igniting a fleeing enemy will usually secure a kill. However, it's not quite as good as Exhaust because it doesn't scale well with level. Using ignite early game will almost always give you a kill as well, and the mastery for Ignite gives +10 AP when ignite is on cooldown, not bad.