Hi everybody, yesterday was a full-caitlyn ranked day, to be honest yesterday was pretty much my first time with caitlyn, I'd already used her but I didn't know really how to so I blowed with her... but yesterday was a rapist day, I really owned every single match I played with her.
I'm at work now, when I return to my home I'll upload some screenshot of my match history so you can see the results I got from this build.

This is maybe not the best guide, but I can assure you that the guide works really great and playing correctly you will carry the game like a boss.

Pros:
- Nuker as my mother's farts(And believe me, they can kill you...lol).
- You can escape from almost any situation with your 90 caliber net(Remember, you can go across some walls with the net, for example, SR Dragon-jungle wall).
- You have a stupid range... 650 is really stupid... TAKE ADVANTAGE OF THAT!
- You're supposed to be the carry, so, act like one, don't try to be a hero, don't initiate, that's the tanks function.
- As the carry, don't doubt on steal kills, if you have some crying stupid noob on your team, just say you're sorry(even if you're not), and keep playing, it's better to assure the kill instead of letting your teammate get the kill giving the enemy a chance to escape.

Cons:

- Squishy as hell.
- Ult can be absorbed for the tanks if they're smart.
- if you're ganked it's practically a death if you have no escape summoners like flash or ghost.
- I can't remember any other cons now, if I remember one I'll update lol.

Greater mark of desolation x 9.
Greater seal of replenishment x 9.
x 9.
Greater quintessence of desolation x 9.

Explanation:
The explanation is kinda simple... ArP marks/quints to make more damage all over the game.
In early game you will be practically doing true damage as you get 25 ArP just with runes, so this will help you a lot in mid lane 'cause you will be able to harrass whoever is lanning against you.

mana/5s Seals will let you use your skills more often as you get mana to use them. You will have mana practically always to use your piltover to farm and harrass your opponent.

MR gylphs, I use them cause in my opinion other runes are not worthed, also you get a really nice amount of MR early game helping you a lot against caster laners like annie, orianna, etc.

Maybe you like more AS instead of the mana regen seals, go ahead, this rune build is the one I use and the one that yesterday gave me a lot of kills, maybe it's not the best but it works.

This spell combined with your 90 caliber net should be a 100% escape combo. It worked pretty nice to me I'd escape from very freaking crazy situations.
This is basically to shoping safe on earlygame and to lane jump late game to blow up turrets. Also, if you have a good jungler/support who wards enemy jungle, you can use it to gank people from places that they will never expect you to.

You can use Ignite instead of Teleport, or Exhaust, but I prefer Teleport over Exhaust/ignite.

Well, I'll explain a little bit of how do I make my buys, when, and that kind of stuff.

When the match starts, grab a Doran's blade and go mid, not much to say.
Focus on last hitting and rush asap a BF SWORD, your first lane leaving should be to buy this, if it is posible don't leave the lane until you have 1650 gold at least to buy it, if you leave with less gold don't buy a ****, wait till you can get that bfs.
If you are farming right and getting some kills you can probably rush IE first of all, If you can't do it, you'll kick everybody's ***, if you can't rush it, go back to buy your bersekers and then buy IE.
After IE you should get a Phantom dancer. Yesterday I'd rushed it fast... with IE+PD you'll farm like a boss and harrass practically every enemy excepet for the tanks(maybe you can harrass them too depending on how fast you rushed this 2 items :P), so it would be a nice and easy game for you. This phantom dancer you can rush it, OR, you can get a zeal and get the rest later.
Anyways your next item should be a bloodthirster, then a last whisper to **** the armors up and if you reach it (I did it in only 1 match yesterday) sell the doran's and get a madred's bloodrazor.

Of course, my guide is almost 100% AD, sometimes, you have to take some situational items, items that may help you to be a little bit less squishy.

I will list some items that may help you a lot in matter of survavility:

= Great amount of life, permanent slow, and 20 AD.
= 40% AS, 30MR(+20 stackeable), and 42 magic damage in adittion.
= 56MR + cleanse every 90sec.
= It's a stupid **** item for me but maybe you like it...
= Great item, 375 mana and health, 50MR and you'll avoid 1 negative spell every 90 seconds.
= Another cool item, 45 armor, 18% crit chance, and a little bit damage, 2% of you max hp, about 20 AD every 1000 HP.

You can use whichever you want, of course you have to analize the situation of the match, the type of enemy champions, etc, so you can make your best mix.

I'll tell you my experience...
Yesterday I've played about 6 rank matches with Caitlyn.

In 4 of them I got mid, in this 4 matches, we won. I creeped like hell, rushed IE so fkn quick, harrassed my counter-laner like hell getting at least 4 kills early game from my opponents.
My damage output was CRAZY.

In 2 of them I got bot with other champions, we lost. I couldn't creep as good as I needed to, I couldn't rush IE so I had to buy some extra Doran's to don't loose the lane... in a couple of words, IT SUCKED.

So, try to get mid lane and for god sake JUST LAST HIT MINIONS!, the less minions you loose, the more damage you will do, the more profit you'll get.

Mid and late game is an instance where I like to roam around my jungle and switching between my lanes to help pushing each one.
My personal choice is to get turret over kills, and the more turrets I can get.
For example if you're pushing top with your whole team and there are minions pushing bot hard, I would probably reach bot with my teleport to get bot turret too.
Except an enemy is very low HP and you have 100% chance to get the kill, focus the turret, if you have that 100% leave the turret and kill da nub, then you can finish the turret.

Your roll, as the carry, it's to blow the **** up on every single squishy enemy.
Do not ever forget this things:
- YOU ARE THE MAIN DAMAGE OUTPUT ON THE TEAM, SPECIALLY IF YOU'RE FED AND FARMED!
- YOU'RE SQUISHY AS HELL, SO, YOU SHOULD NEVER, NEVER, ¡¡¡NEVER!!!, BE IN THE MIDDLE OF THE FIGHT, THAT'S TANKS FUNCTION!; YOUR RANGE IS INSANE; SO TAKE ADVANTAGE; HIT AND RUN WITH YOUR 650 RANGE!
- NEVER doubt about spamming your Q, that skill does insane amounts of damage and it hits several enemies if you use it right, so taka advantage.
- Use your ult right, try to cast it on an enemy who can not be protected.
- Don't be a hero, you're not Jax (Lol), you're caitlyn, if your team dies, gtfo of there, It's better to stay alive and have the chance to protect a turret instead of dying pointless. This does not means to leave your team to die... it means that you have to run ONLY if it is a 100% loose.

Well, if you reached this point, Thanks!.
If you didn't, GO F*CK YOURSELF!, hahaha Just Kidding, I hope you can get profit of my guide, I promise to upload a ScreenShot of my match history from yesterday, I think that my matches went something like this:
4-2-6 - WIN(mid lane).
8-4-6 - WIN(mid lane).
6-7-9 - LOOSE(bot lane).
14-2-8 - WIN(mid lane).
18-4-12 - WIN(solo top lane against 2).
14-14-18 - LOOSE(bot lane).

But I promise some proof.

well thanks to read my guide and if you have some question or something, add me, my summoner name is NagOrth and my skype is xJotah

See you everybody!

P.S.: I will update this guide if something comes up.

Updates:

August 17: Added Situational items explanation.