Please dont mind any misspelled words or typos, and sorry if I typed a bit too much to read.. I have been using this build I made myself for quite awhile so I know it works very well, a friend of mine said I should post it here so I'll try my best to explain it all... If you have any questions, feel free to ask here I'll try to get to it when I can, or if you want to look at my character in game or my match history my name there is "Neko Mae".. Without the quotes of course..

This is a first draft and my first time posting something here so sorry if its not set up too well, and again, any questions or sugestions just let me know please.

Before you rant about my summoner spell selection, allow me to talk a bit about them.. Keep in mind that this is a pure Support build for Soraka, that being said, a smart enemy team will constantly try to focus you down threw out the game.. Revive is a rather nice counter for this, and as far as scaling into late game it only gets even better as your level and death time increase. Having the mastery for it gives you bonus health for 2 minutes, and lowers the recharge time on it even more along with the Presence of the Master Mastery. Using Revive and then your Ultimate if you could not use it earlier to save allies still in the team fight can also lead to wonderful results.

Secondly I usually take Fortify, this oftain under-rated summoner spell can be great if used properly, the best time to use this spell is while an enemy is trying to tower dive you or a teammate, making them take alot more damage then they thought they would. This is just a personal preferance and I know its not for everyone so I'll list others that are good for Soraka support, and what's bad for her aswell, however I still recommend always keeping Revive and it's mastery.

Keep in mind that if you choose to get one of thies summoner spells, you can move 1 Mastery Point out of either Perseverence or Hardiness in order to get the Spell mastery.
Other good Soraka summoner spells include:

Ghost, to either run away from enemies or to get over to heal your allies before it is too late..

Teleport, to move great distantes much faster to either protect a tower, or get to your teammates fast.

Clairvoyance, to check for enemy status, avoiding ganks or setting one up with your team..

Summoner Heal is somewhat acceptable, but I personally never use it on Soraka, with two very powerful heals already why waste a summoner spell slot on a third that dosnt scale well late game?

Think outside the box a little for this one, Smite may be a good choice for Soraka aswell if you get the mastery with it, as a support your minion kills will not be very high, but the more gold you get the better.

If you really like Flash or Cleanse, they might be useful too, however I wouldnt recommend them over the other options.

And PLEASE do not, no matter what, DO NOT use Clarity. You have a re-useable mana recharge button at all times with Infuse, use Infuse for mana, not Clarity.

The reasons why I selected the Runes I did is as followed:

Quintessences, Gold per 10 is one of a support Champ's best friends, I cannot stress enough how useful gold per 10 is to support champs and champs that have trouble farming minions.

Marks, Don't really need magic pen because you're main focus is not damaging the enemy, but healing your allies.

Seals, Personally I find the healing to be powerful enough as is so getting some defensive runes here to try and help keep you alive is a good idea.. a dead Soraka can't heal. However, if you don't think you need the extra defense, more AP per level runes would be good here.

Glyphs, Cooldowns are very importaint for Soraka, what more can I say? She does not need any more mana or mana regen because of her Infuse ability, but more cooldowns means faster heals and faster mana recharges.

I always start off with an Amplifying Tomb, and go back to base using B as soon as I have enough gold to upgrade it into Kage's Lucky Pick, upgrading it as soon as possible is VERY importaint, because the sooner you have it, the more money you'll have. And always keep in mind, as a support champion you will not get minion kills easily, so gold per 10 helps out tuns.

After getting the Lucky Pick, I usualy end up staying in lane for a rather long time, wich is rather easy to do as Soraka because you can heal both HP and MP of yourself and your laning partner. Also keep in mind when neither of you need mana that your Infuse doubles as a good Harrassment spell if cast on your enemies, and sometimes can be used defensivly to silance them.

When I go back, I usualy pick up a Kindlegem for life and Cooldown Reduction, and Boots or Ionian boots. Cooldown Reduction should be your first focus as Soraka after your Gold-per-10, the reasoning for this is simple, Soraka's heal, Astral Blessing, and Infuse, both have a somewhat long recharge time to them, but Astral Blessing naturally heals for a fairly good ammount without needing much Ability Power, so save getting Ability Power items until after you have your cooldown items done first.

Finish the Kindlegem into a Soul Shroud after finishing the Cooldown Boots and then work on Ability Power items, I start with a Needlessly Large Staff to later turn into a Deathcap. Next, I usualy work on making Will of the Ancients to not only boost my own AP but to give AP to my allies as well as give them spell vamp, making them live a bit longer as their own spells heal them some too along with your heals.. Generally speaking the match usualy ends around this time or somewhere around after getting your Deathcap, but if the match continues just keep getting more high AP items like the Hourglass starting with the needlessly large staff..

ONLY after having all your slots filled with other items should you consider either upgrading the Kage's Lucky Pick to a Deathfire Grasp, or to sell it and buy something else in it's place. Also, with no other items to buy, dont forget to get Elixirs as needed.

So, how much healing does this build do? In an average match between 40 to 60+ thousand healing done, W healing for around 700+ and R healing for over 1000 to every ally champion on the map.

This is of course based on an average full length match, wich time can vary, and not really counting if one of the teams surrenders early.