First off, I'm not the greatest Lux player in the world, and I don't intend for this to be the best build in the world, I've built it to accomodate my needs. That said, I appreciate all critism, just try to keep it positive.

I've implemented a sort of three stage build. The first part focuses on mana regen, as I tend to cast too often. I find as a midder the longer you can stay in mid without having to go back for mana, the better. After that, I focus on cool down times. My build is set up so that you start with 5% cdr from runes, and will have 30% by the time you've built the third item. From there on, I focus more on AP (and a little spell vamp for sustainability)

My costs are probably a little too high, I'm not sure, but if you can actually finish the build out you should have a good amount of AP, max CDR, and mana should never be an issue.