I find it very difficult and diversial to build items for soraka.
I was going few ways with clarity/flash, ignoring mana regen and just relying purely on AP(two kage's lucky picks, zhonya ring), then my heal was really GREAT, when you have 200+ AP you heal really well.
However then you have mana problems.
I still struggle all the time with items, i was getting archangels now and taking clarvoyance with flash, being more support, i had no mana problem but had very huge gold problem, i usually never make zhonya ring, i just make archangels, i buy two blasting wands and match ends before i finish zhonya. creeping is totally horrible with her.
I was also thinking about buying mana manipulator and innervation, but i dont find extra +50hp heal and 20mp recharge very amazing when i heal or recharge mana, and then i have less AP again.