The reason you rush Rod of ages are becouse you should stack it as fast as you can. It takes 10 min to full stack and its a great item it gives you 100 ap fullstacked wich is one of the items who got the most ap in the game deathcap and fullstacke Mejai's got more. The item you can have if you don't want a Rod of ages is a Sonya's Hourglass but if you want that instead go rush Kage's lucky pick.

There are two things I dont like:
1.There is no collour in this guide. I'll put a link to a guide how to make a guide(sereously this is the best thing on mobafire)

2.Why rush Rod of Ages? I mean why would you even buy it on Lux?? She is a long ranged champ, so why would she need it??

Im not gonna downvote because I see that this is your first build and I see potential in you. I think that this build is going to be high.

http://www.mobafire.com/league-of-legends/build/making-a-guide-101506