Lux is my fav too, how do you like to build her?
Did you see the Hourglass and DeathfireGrasp changes on PBE on ReignofGamging?
No, what changes? :/
My build changes quite a bit, neither DFC or Hourglass are guaranteed it depends on the setup of the opposition.
Core items for me are Athene's Unholy Grail (first full item, that mana reg is too useful to Lux), Archangels Staff (second full item) and Rabadon's (third full item)
I build Archangel's pretty early because it gives plenty of time to 'evolve' it, and Lux with Athene's is spamming a lot of skills so it doesn't take long .. that mana shield late game is <3
Other items
Sorc boots (obviously, they get built depending on the situation - early on if im getting ganked a lot / getting no support or if the lane phase ends early, otherwise its not a priority)
Void Staff (decent enough AP, nice MR reduction)
Lich Bane (decent stats, nice burst thanks to the passive)
Void Staff is the one that gets swapped out depending on the situation - Char's with lowish MR but high health (Cho, Olaf, Singed) and I tend to swap for a DFG. Bursty team compo's that im struggling to stay alive and ill swap it for a Hourglass.