What Health to AP ration is ideal for Soraka?

Soraa is quite interesting when it comes to how you build her. Since her W is locked at 10% max health, it is regardless of how much health you have. But, her Q can only heal her based off of a flat base amount + 5% ap per half second. So the more health you have, the smaller the percentage your self healing restores of your max health.

What is the optimal ratio of health / AP? Do you go just full AP with no Health items? Or somewhere in between?

Keep in mind that some items that she synergises with (either support, AP, HP regen, etc...) give quite a lot of health as well.