Welcome to my champion guide to Soraka, the Starchild.

This is a very specific build, the main objective, enabling Warmog's Armor at Lv. 14, so you can heal your heart out, spamming neverending Astral Infusion.

Quintessences: 3x Gold, or 3x Health Regen
Marks: 9x Armor, or anything else you might prefer.
Seals: 2x Scaling Health, these 2 are vital for the purposes of this build, granting you 37.24 extra health at level 14, which is when you want to be finished with your core build, 7x Gold.
Alternatively you may prefer extra armor, or mana/health regen, feel free to switch these up.
Glyphs: 3x Mana Regen, 6x Scaling Magic Resist, again, these are to your personal preference.

5 points on Veteran's Scars are a must for the purposes of this guide, granting you 45 extra health, anything else you can move around if you prefer, i'd heavily recommend Windspeaker's Blessing , though.

With the build provided, at level 14, you'll get just enough extra HP to cross the 3,000 threshold, totaling at 3,005 HP, enabling the Warmog's Armor, plus 45% CDR, leaving Astral Infusion on a super short cooldown. If your game actually goes beyond the point where you have all these items, feel free to round it up with whatever feels best.

Core Items:
Eye of the Oasis
200 HP, 10% CDR, + Mana/Health Regen. Great for the early game, even more so since wards are scace this season. This should be your first completed item, followed by:

Ionian Boots of Lucidity
10% CDR, +10% Summoner Spell CDR, Exhaust will have around 2.5 min CD with these, make sure to enchant these in the lategame, with whatever feels best for the current situation; next up:

Locket of the Iron Solari
400 HP, 10% CDR, Magic Resist aura for the entire team, and a GREAT active for teamfights.
Go for Aegis of the Legion right after the boots, then complete this one. I would recommend building this even if your opposing team is mostly AD based, since the shield from its active can be invaluable if well timed; afterwards:

Mikael's Blessing
10% CDR, Tons of mana regen, and another great active for teamfights, even though it has a longer cooldown than the Locket. It has one of 2 purposes, first, to save a teammate from a crucial CC, and the other, and i can't stress this one enough, to heal yourself so you can keep dishing out heals earlygame. Finally, last, but not least:

Warmog's Armor
850 HP, and an insane amount of health regen, provided two things happen, first, breaking 3,000 HP limit, and, second, not taking ANY DAMAGE. Again, you'll achieve 3,005 HP at level 14 with this build. Which leaves up one spot to round up the build; some options are:

AD Heavy:
Randuin's Omen
Thornmail

AP Heavy:
Spirit Visage: 10% CDR Overkill, might want to switch out boots
Banshee's Veil

Utility:
Ardent Censer: Wish gives its passive to the entire team, mostly good for AA based champions ( Vayne / Kog'Maw, etc), also, CDR overkill, so, switch out boots.
Rabadon's Deathcap: For stronger heals.

Not Recommended:
Rylai's Crystal Scepter: Starcall Already slows, so, not very useful.

Priority:R > W > Q > E

R: Wish
Let your teammates know when its available during the laning phase, so you can help other lanes dives/ganks. During teamfights, try saving it until at least someone is under 40% HP, so you get more of a benefit from it, basically, don't burn it too early.

W: Astral Infusion
Your bread and butter. Try not to overheal your carry during laning phase; Pre-level 14, try to stand as safely as possible behind your team mates, so you can dish out as many of these as possible during a teamfight; consider it a success if you're backing with 1%~ish HP, that means you healed as much as possible, while skirting around the edges of the teamfights. After lv. 14, with the completed build, you should still aim to take NO DAMAGE at all, since taking damage disables the Warmog's Armor passive for 8 seconds, so, in conclusion, be as cowardly as possible when it comes to teamfights, while still dishing out the heals from Astral Infusion.

Q: Starcall
Mainly used during laning phase for self-sustaining purposes, although somewhat weaker to its previous version, the slow is now for the entire hitbox, with the new changes, it boosts the power of your Astral Infusion, if you manage to land it. Its much cheaper now, so feel free to spam, but try not to hit that many minions, unless you and your ADC want to shove the lane. It doesn't really add that much damage, so, don't overextend trying to land these if it means you'll take harrassment in the process. It is now superb for kiting during teamfights, especially if a bruiser or assassin comes for you, land one Starcall, and you'll both slow them, and speed yourself up by 15% while moving away from enemies.

E: Equinox
Big AOE silence, useful for many things - cutting off escape paths: place it ahead of the enemies, making them either sidestep it, or risk getting snared by it; hindering assassination attempts: all-in assassins ( Zed, Akali, etc) will try to either get to you or your ADC, place Equinox right below you or your carries' feet, so their damage output is lowered (also a great moment to Exhaust them); interrupting channeled abilities ( Miss Fortune, Katarina, etc), and in general, wreaking a little bit of extra havoc during teamfights, placing it either near you, to avoid getting focused, or under any relevant mage in the opposing line-up.

Still a work in progress, anyways, these are the basics, so, might as well post it already :)