I'm confused as to why you take heal, Soraka's a healer so it seems a little redundant, but to each his own I s'pose....
Starcall is important early game because it's the only viable farming ability Soraka has other than last hitting with her basic attack. It also hits extremely hard at first level because very few champs have high MR at that level. If you starcall then infuse you will deal more damage (because of starcall's MR debuff).
I go flat magic pen in reds, armor in yellows (Soraka is squishy and gets focused often) and AP/level in blues for runes.

I ramake it, I start with tears of goddes now it does 1000 mana and I dont need clarity, I take a tird heal and it work too good

Don't waste points in Starcall at the beginning, and try start with Infuse in the start for Silence to get an easier First Blood.

Your rune setup seems abit different than mine, I just go for pure AP. I might try MR later on, but don't got a plan for it atm.

I don't think I got anything else to say about this build. I rarely have to get defensive items. Because my teammates never let the enemies come close to me.

Other than that, it looks like a fine build to me.

Thumbs up!