This is how i play Caitlyn, i kinda want to end the myth that caitlyn sucks lategame. With this build you will be able to spam your abilities, ithink pileover peacemaker will have like 3.6 second cooldown and deal around 700 damage, thats pretty darn good. You will be able to harass for ages without any real risks. Ace in the hole will have like 35 sec cd, so use it :O.

With this build you wont do insane damage, but you will do good damage and without any real risks, sure you can die and you will die :D but you shouldnt die as much.

Armor penetration runes to deal more damage, rather basic.
HP/LEVEL since Caitlyn got rather low total hp, this will help a little.
CDR since its kinda the whole point with this build, its about using your abilities rather then autoattack.

23/6/1, well not much to say there more then that i go for archiac knowledge in the offensive tree. This is beacuse the traps deals a nice amount of extra damage, so its not a bad choice.
Point with getting all those points into offensive tree without getting any crit-items is beacuse of havoc. 5% aint much but its really needed in this build, i have played around with the utility tree as well. 6 points into the defensive tree seems a bit random but its a nice earlygame boost, and 1 point in utility is for that extra ghost effect.

Ghost and Flash, why? not dying is kinda what i go for with this build.

Meki pendant and health potions for a starter, this will help you stay in lane for some time. You need to collect the gold for Manamune before your first recall. Manamune is the key item in this build beacuse without it you wont be able to spam as needed in order to do good.

The core is Manamune, Ionian boots of Lucidity and Last Whisper, Glacial Shroud.

Not the cheapest core there is but its effective. However after the core it all depends on what you need, i usally go for a B.F sword just too boost my dps a little. However i really fancy defensive items, survival is the key. If they got some nasty melee guys i go for frozen heart right away.