I need some Ezreal help

I bought him today wanting something new for the ADC role. I read two guides and played a few games - i have some questions. In all three games I built first then . I'm not seeing LB in any guide and I'm not sure why. With this run up, he seems to be a late game champ. I took the masteries I thought were best and am running Mage/Support runes for gold generation.

Having said this, why wouldn't you want LB (according to the guides) and what do you usually start with? Furthermore, why would you go AD when it looks like it only helps one of his abilities.

Thanks, Rook