Short answer: She's very niche. but she works. Honestly, there are better picks than her even in her niche environments, but she works, and that's good enough for me.
Long answer: Soraka is basically a utility mage. What I mean by this is you build AP(
,
, you name it just don't forget your
) and that's how you get the most out of your abilities. You are pretty much forced to do this because:
-
Your W scales with your maximum HP; no about of health,armor,MR, whatever is going to stop you from killing yourself, and your health regen is garbage. The only way you can keep yourself alive is by healing lost HP by hitting Q's. The health you get from Q is a flat number that scales with the % of HP you're missing, but falls off hard later into the game. Building AP keeps the number respectable and gives you hidden durability.
-
You want to use your W as much as possible; If you're building CDR (and you will build CDR), you're going to kill yourself VERY quickly. At the same time, you're getting more use of your Q more often, which lets you potentially restore any lost HP, but as I said above the base numbers are very low; so you want to abuse the strong AP ratio by building AP.
3)You want to get the most out of every W cast More AP=stronger heals=More health restored per health lost from casting the ability in the first place.
and 4)**If you don't build AP, Your healing gets outpaced/falls off very quickly.Your healing stops scaling at level 9, and the enemy carries are building damage until they hit 6 items. **
Some things you want to know about Soraka when picking her would be the following:
Does my team have 1-2(or more) champions that armor/ resist stack? Tanks like
and
love to build armor and Magic resist, meaning that healing is EXTREMELY effective on them since it's,well, external Health. Your heals get extra mileage on these champions and drastically increases their durability!
Does my team have champions that can give me space to "work my magic"? When I say this, I'm talking about champions that can hold the line for Soraka so that she can stand behind them and safely heal. Basically anything that's durable and limits what people can do through CC. Again, Tanks like
and
are good walls for Soraka to keep her squishy body behind while she does work.
Finally:
**Does the Enemy have "exploitable threats"? ** This is more of a varied topic, but Soraka "counters" quite a few champions. I'm not saying you should auto pick her when these champions come up, but she does well against them.
is just an example. Irelia's passive is quite redundant against Soraka because her E is a field that is consistently on Irelia, and her main way of keeping her teammates alive is through healing, not crowd control.Most top laners are also taking
, so they won't be able to shut you out, or make you waste your Ultimate with 
That's about all I have to say, If you have any questions, don't be afraid to ask!