Support Item builds

What does a Support build, and when? I understand that the items are determined by the enemy champions, and what they are doing; however, I'll see supports primarily start off with the same things (sorry, I can not remember/do not know what they are called): * blue knife thingy (supp that *pew pew*) * Shield with green background (supps that "hit" people) * green/purple/other purple eye-thing * Bell looking thing * Bird (phoenix?) thing Is there anything after that, or is that where it becomes champion specific? If it helps narrow it down, right now I primarily play as Soraka, but last year I was into Janna and Lulu. Also, which summoner spells? Or is that also dependent on opponents? I think I mostly use exhaust and flash. As for Masteries, are they also dependent on the match, champion, or position? Which ones should I focus? I was told to hold off on Runes until level 20, plus I don't have enough currency for them.
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