My build isn't what most people do, but I like it and it works well for me.
My build:
9x Magic Pen Marks
9x HP/lvl seals
9x CDR/lvl Glyphs (15% at 18)
3x CDR/lvl Quints (15% at 18)

You just spend the whole early game doing nothing but farming Q. Don't roam, don't try to get kills. Just play safe and farm Q.
I usually end up with 1200+ AP endgame and have 40% CDR. Plus a mana shield. Lich bane gives you 10% cdr and runes give you 30% CDR. Plus when you have that much AP your lich bane procs over 600 extra damage.