...and it won't let me. It says the only prereq is base attack of +1. Well my rogue has +1 melee and +5ranged so I meet that right? Why is it grayed out?
Base attack bonus ( BAB ) +1 and melee +1 are not the same thing . Bab for a rougue grows +1 every 2 levels. Melee bonus is given by strength ( probably your rogue is level 1 and have a 12 Strength ). Hope this helps
No it grows +3 every four levels. Every first of four levels (1, 5, 9, 13, 17) doesn't increase your base attack bonus if you're a rogue, cleric, druid, monk or bard. That's called medium bab. Wizards and sorcerers gain an increase in base attack bonus every even and nothing every odd level. That's called low bab. Everyone else's base attack bonus is equal to class level; high bab.
I do apologyze for the unintended misinfo, Zugschef is right. What I actually meant was that your rogue will have the BAB +1 at level 2 , meaningm you can have weapon finesse at said level.