Hello Mobafire Community, this is my first Guide but I've already played LoL since some years and I have seen that there were no AD Soraka build and I needed to do it with 4 other AP Carries in my Aram-Team, and it was actually pretty nice. Pls note that it's a fun-Build and should not be used in Ranked Games. This AD carry build is made for Soraka to tumble into Teamfights, irritate them with Silences
!As the Pro Guide crafter I'm not it will need some time for Visual improvements, pls considerate this while rating this Guide!
!The stats dont show the additional mana and attack damage by full stacked Manamune!

Pros

awesome amount of Heals
running Mana Potion
spammable Silences
Nice Autohit-range
annoying Mr-reducing Rain
awesome Anti-AP passive
She throws Bananas (what do we want more)
Everyone will underestimate your Damage
Awesome Sustain

Cons

Weak Earlygame
Closely 0 CC
Some Mana-Dependance
Ignite makes her useless
AD defined as Trollpick
No burst Dmg
Weak early game farming

For Runes i take

Flat Armor Penetration Marks to prevent getting useless when Enemies stack Armor, at all common AD Carry runes.

Health-per-lv Seals to give Soraka some more sustain for the teamfights.

MR-per-lv Glyphs because she will be vulnerable to AP-Burst lategame.

1,5% Movement Speed Quintessence is a must go to fill the gap of CC, to give Soraka chances to keep up with pants-peeing Runners or to escape close Situations and Ganks.

For masteries i take 21-0-9 to maximize my Dmg output, CDR Reduction, Movement Speed and Mana for my Manamune

As Summoner Spells i take Flash and Exhaust.
Flash is the most used Summoner Spell in the game, helping you to do final strikes or escape sticky situations and ganks, general for gap closing
Exhaust is important to fill Sorakas lack of CC or winning botlane fights (always to use at enemies AD-carry as it lets him miss all his auto attacks), also good for hunting down or running away, always can turn around an 1on1 fight.
Other viable summoner spells are Ghost, Ignite and Heal

The goal for midgame are the cor items Ionian Boots of Lucidity, Manamune and Trinity Force, giving me nice Dmg, CC and Sustain
I start with Tier 1 boots and 3 health pots giving me the needed speed for kite-harass and lasthitting minions in early game easier, another possiblitity is Dorans Sword. With the potions i can stay in lane long enough to farm gold for my next item, Tear of Goddess (every spell gives you 4 additional mana up to 1000); which gives me a huge amount of mana for spamming heals and giving me a huge amount of Mana for Manamune.
Next I'll buy 2 Dorans Swords to arise my early game strength. After that I upgrade my boots to CDR-boots so i can spamm more heals and silences.
Then i upgrade my Tear to Manamune, one of my core items because of its awesome passive. 2% of your Maximum Mana will be convertet into Attack Dmg. With your full build and the full stacked passive of your Tear (Manamune keeps it) your Maximum Mana will be over 3000, giving you an awesome additional Attack damage of over 60.
Trinity Force will be my nex core item, giving me everything Soraka needs: More ad/ap dmg; more sustain; awesome Dmg- and Slow-passive; AS; Movement Speed etc. .
Then I buy Glacial shroud for nice amount of armor, CDR-spamm and more Mana, after this Bloodthister, which gives me awesome amount of dmg and nice lifesteal as the AD-Carry Soraka is.
Then buy Banshees for spell shield, MR and more Health and Mana. Last, upgrade your Glacial into Frozen Heart, giving you evn more Mana and Armor and an awesome Anti-AD passive!
Other viable Items are Infinity Edge, Last Whisper and Phantom Dancer

I'll begin with my Heal, giving me more sustain and reducing their AD-carry's dmg output.
Next Infusion for C-C-Combobreaking their abilities or just if my mate goes oom.
Then 1 stack at Starcall to stack up my Tear. Take your ult whenever its available due to its awesome Team Heal and to reduce its Cooldown. Meanwhile I'll maximize my Heal first, because Soraka has no AD-made spells and this is countering their AD-carry. Then infuse to spamm longer Silences and deal more dmg, and the rest is for starcall, because I wont need it much !as I concentrate on Autoattacking instead of permament Rain-spamming!.