I have a bunch of different builds for Soraka.. Rune setup is pretty much always the same.
Summon Aery
Manaflow Band
Absolute Focus
Scorch
Font of Life(some people prefer other runes but I like this one best personally)
Revitalize(a must)
Adaptive
Adaptive
Armor
Favorite item build that works well into pretty much everything:
Relic Shield(different yes, but for a good reason)
Ionian Boots of Lucidity
Redemption
Shurelya's
Warmog's
I like to get Relic Shield when I know I'm going to be preparing for Warmog's after Shurelya's. It basically guarantees that I'll have the 3k hp for the passive to kick in when I finish building it.
Last item honestly doesn't matter. If you do well, and you are able to finish Warmog's early, the game should end as a direct result of picking up that item. Your team will be able to push and pressure endlessly. Game should end by 25 minutes if you get it at any time before then. If you only manage to finish the Warmog's when its getting late ~30 minutes more or less, it will be more difficult to end just from finishing the build, but that doesn't mean you failed either. It's still completely viable. All this means is that you missed the mid-game breakpoint where Soraka can end games by herself. She can end games by herself mid-game because most Team compositions can't last long in extended team-fights at mid-game. Warmog's Soraka ensures it so that her team CAN, regardless of the composition. It's best at mid-game...but still very much useful and worth having late-game. Just kind of sucks when you miss the perfect opportunity to carry/end/win game by one team fight or just a few minutes.
Another good build is Redemption into Athene's. Then Shurelya's.
Some Sorakas like to use Ardent, but I personally hate that item on her. The only other support item with healing% I'd consider getting other than Redemption, Athene's, and Shurelya's is Mikael's...and I'd only get it if absolutely necessary. Normally, I'd expect the ADC to get QSS...so unless I feel like I might need it for something specific to help my whole team and not just ADC, I'll probably skip Mikael's and get the Redemption/Athene's combo instead, which is the most tried/true to work. It's standard... You can also build into Warmog's way late, but it's unlikely you'd ever get it before the game ends if you go that item route. There are different orders in which you can get your items...just do what you feel is natural for you.
Oh, and only get the Relic Shield if you KNOW you're going to do the Redemption/Shurelya's/Warmog's build.
Otherwise, always go Spellthief's Edge.
Relic Shield was buffed for ranged attackers, so that it's easy to get cannons/last hits. 30% HP left...easy. Also there's no benefit to getting Spellthief's either in terms of damage anymore. Shield doesn't heal anymore either so...when it upgrades the first time, you get the full 50% hp execute same as melee. It's easy to upgrade. Just make sure to keep track of when the cannon waves are coming, always leaving at least 1 charge to get it...If you consistently miss the cannons, you're gonna get it real late, and you'll almost certainly not finish warmog's before 25 minutes.
Oh.. and skill order.
It used to be Q > E > W .. have 3 points into E by lvl 5, then max W by lvl 10/11. Then finish E and max Q last.
After the rework/changes you're gonna want to do the opposite. Q > E > W .. then have 3 points into Q by lvl 5 and max W by lvl 10/11. Finish maxing Q afterwards and E last.
The early levels of E were lowered by a LOT, so it's not really necessary to get points into it to lower its effective cooldown by mid/late game.
Also, since Q was given a higher cooldown at lower levels, and cdr reduction per level, putting points into it is a bigger priority. Even more so because the rejuvenation effect was buffed immensely. Remember, as long as you have the buff, no matter where its at in its duration, if you W someone, they get the FULL duration of the rejuvenation too. Rejuvenation heals for around the same amount as the heal itself...so if you've been using Q effectively and have the buff on you, your W will always be healing pretty much twice the amount. the amount healed from Qs rejuvenation also goes up per rank put into it, which is the main reason to be putting points into it over E.
Anyways, hope this helps. GL.