Lux is a safe champ, always sitting behind everyone else, has a slow, a root and a shield, pretty balanced support. Item-wise, I always build RoA, sorc boots, Arc staff, deathcap, morello's evil tome, void staff, getting some pretty high stats in HP,MP,AP,Mpen and CDR. Imo that's all you're ever gonna need as a caster
Currently playing some ranked games, had a very unexpected win yesterday, mainly due to our team comp (Alistar,Galio,Lux,Morganna, Xin Zhao) versus an actually balanced team (Amumu, Kata, Kennen, Garen, Irelia). Although Alistar failed as a tank, and Kata got fed (3/0/0 or so at first TF), I picked up a lot of kills as Galio and managed to carry the team a few towers in.
OTOH, lost a game thanks to a terrible kog feeder (0/7/1 and FB) who wouldn't mid against Ezreal...sometimes I really wonder if 4v5 is better than 5v5 w/feeder on the team.
EDIT: Speaking of builds, how is this for Shen?
I've also tried AP tank, but didn't work out so well...