This is how I'm building Lux since the changes to Zhonya's/Dorans and the new additions of Ionian Boots of Lucidity and Morello's Evil Tome. Seems to me this is the most efficient way to get both high AP and great cooldown reduction. What I've listed here is my core build... if the game is still going after I have all these items, I usually pick from the following items based on the enemy team comp: Zhonya's Hourglass (if they are targeting me effectively), Void Staff (if they are stacking MR), or Banshees Veil (vs. pests like Karthus or even another Lux).

To explain a few choices:

Clarity vs. Flash: This is mostly a matter of playstyle. I like to play very aggressive and harass heavily in the early game. Clarity allows me to do this without starting with a mana/mana regen item. Instead I build an amplifying tome into a meiji's early and hit a lot harder in the early/mid game than most Lux. I personally feel like with all Lux's CC I rarely need flash.

Boots: I go with the CD reduction boots most of the time but if I am playing a particularly tanky team, or if my team is loaded with AP (making the other team more likely to build MR), I sometimes go with Sorc Shoes. This is a judgement call based on the opposing team's MR. Most of the time I feel like I have enough magic pen through my runes and masteries.

AP Quints: I ran flat health quints prior to the nerf but now I've switched to AP quints and I'm loving it. Starting with amplifying tome and +15 AP from quints is like starting the game with a blasting wand. I'm able to harass really effectively early and often kill an opponent from ~40% HP right when I hit level 6 and get my ultimate.