Always build a sightstone... Can't stress this enough. Majority of games are lost because lack of vision. Don't support if you aren't going a sightstone...
Redemption... I personally build Redemption on every support. The almost global heal is basically a Soraka heal. Plus you can use redemption to secure some kills.
Locket is what I usually build second. The huge shield can be a game changer.
Athene I rarely build but you can get some damage letting athenes stack and dash back for a massive heal. I don't build this because I feel we have enough cdr.
ZZrot for some armor and mr while pressuring a lane.
Boots you can sell lategame (only if you dont have any space left) because the zzrot/talisman gives enough movement speed. Use the talisman for the burst movement speed.