I'm not talking about "offense or support" in how you build her but in how you play her.
obviously lux needs to build AP and as much of it as she can manage, but that doesn't necessarily mean that she should be getting a good chunk of farm with which to do it. Sometimes you can play lux bottom with a carry and use her nuke + autoattack harass to win the lane for your ally. In which case they are getting all the farm but you are using lux's skillset to be super useful and win your bottom lane.
You end up building her the same (as you eventually manage to get the gold to fund yourself), but your early game focus is on your team dynamic rather than farming for yourself.
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Eff_Dee
http://img.imgcake.com/nio/9fdpngys.png