The reason I go with this build is because it gives Soraka the best CoolDown options available. Along with the item build planned out you'll reach 39%CD before mid-game which will lead to a lot of QQ and mid-game surrenders given you have a solid team makeup. I prefer ghost/flash as they give me all the survivablity I need. If you find yourself dying while playing Soraka its most likely because you are not keeping your distance. Distance is the key to success with Soraka, thats why with ghost/flash+movespeed mastery+boots of swiftness this shouldnt really be an issue. If you somehow manage to make it into late game 40+minutes your team is doing something wrong. You'll be healing for over 750 health every 5.5 seconds and have a global heal doing over 1000 health every 40 seconds. If facing teams with casters like Veiger/Fiddlesticks be sure to silence them with infuse once your tank ingages for a easy shutdown and quick 5v4 outcome. Stay on top of healing the main dps carry and tank over any other champions. Dont be to conservative with using your ULTIMATE if it can save your main tank and or dps carry. Farming wise try to last hit with your AA/INFUSE/STARCALL. Most importantly keep your LANING PARTNER ALIVE before anything, I have seen way to many noob sorakas leveling up starcall first only healing themselves and not knowing when to use infuse.
If your finding yourself having mana issues which you shouldnt because you have Infuse buy a Tear of Goddess but honestly just try and learn when to use your infuse on either yourself or your laning mana champion if you have one.
Any questions please post and I will respond as soon as I can.