Hi everybody! This is my first build, and it's on my main, Caitlyn! I feel that Caitlyn is one of the if not the best carry out there. This is mainly for her unmatched range ( except fot Tristana), and her Q which is great for farming and nuking champions. If I make any mistakes or you have any suggestions please leave a comment below.

Pros:
Great Range
Crits combined with headshot = AMMAAZZIINGG
Good finishing ultimate
Farming is easy with her Q

Cons :
Very Squishy
Focused a lot
Shut down easily with CC
Not the best in team fights if you dont know how to use her

Caitlyn's Q is Piltover Peacemaker, a long range nuke that is great for farming and using in team fights or even in 1v1's. This skill does next to nothing late game on beefy champions but it is essential early game for farming and harrasing.
Caitlyn's W is Yordle Snap Trap. Caitlyn sets up to three traps which trigger on champions. When sprung, the trap immobilizes the champion, deals magic damage over 1.5 seconds and reveals the target for 9 seconds. Traps last 4 minutes. These traps are so useful, when in mid you can place them in the brush so you can see if someone is trying to gank you.
Caitlyn's E is 90 Caliber Net. Caitlyn fires a heavy net to slow down her target by 50% and deal magic damage. The recoil knocks Caitlyn back. This ability is very useful. You can either use it as a small blink to catch up to get that last shot on a champion, and use it to run away from a gank.
Caitlyn's R is Ace in the Hole. Caitlyn takes time to line up the perfect shot, dealing massive damage to a single target at a huge range. Enemy champions can intercept the bullet for their ally. It provides vision of the target for the duration. Im not going to talk about this much since I do down below.
Caitlyn's Passive is Headshot. Every 8 / 7 / 6 attacks (attacks while in brush count as 2), Caitlyn will fire a headshot, dealing either 150% damage to a champion or 250% damage to a minion. This is a great passive, it like a critical every 8-6 attacks and is great for farming, harrasing, and getting that final blow that you wouldn't had been able to get had you not had this. This passive combined with infinity edge and a critical= massive damage.

With Caitlyn I like to takeand. Now people might say "No she needs ghost because she already has her net." Well they're wrong, ghost doesn't do anything, sure it gives you a speed boost but if you walk into a bush and find three other people in there, ghost will not save you. However, flash combined with your net will get you out of most any situation.
Exhaust is good for 1v1 and running away.

Other options include, for when you know your ult wont finish them, get close and ignite them, then ult for the kill.

Although I don't take this,might be good for catching up do cast your ult, but flash also does this a lot faster.

I go with the 21/0/9 build for Caitlyn. Taking some cooldown reduction in the offensive side to make spamming her Q more effective. Also, in utility I take that one extra gold over the 1 extra mana per 5 seconds or the extended neutral buffs because to be effective she needs items and this helps her get those.

For marks I go with Desolation marks, giving her the needed armor penetration.

For seals I go with attack speed because I like the early game advantage against other carries, but it's really up to you about these.

Glyphs you need to go mana regen. Cool downs are pointless with Caitlyn since they only noticeably benefit her Q, giving her better farming, but since the cooldown is already so low I feel like there is no point in getting these.

Quintessences I go for Desolation to add more armor pen, these will give you even more of an early game advantage.

I start out with a, I feel this is the best choice no matter who you are facing because Caitlyn needs more health than she already has and with your armor penetration you don't need any more attack damage than the Doran's Blade gives you

After that getand if you can a. Now instead of upgrading the scepter into a, get asince it is more essential early game against carries or just any other player, it will get you more kills than a Bloodthirster would.

Now get anto add to your attack damage. By now, you should be killing people regularly without dying to much. Remember, if there is even one person missing, don't turret dive or even overextend near the other person's tower, you will die.

Then get afor attack speed and movement speed, while the crits also help. Then get ato add to your survivability, although you should not be dying that much, or at all. Finish your build off by completing the. Your build is complete and you should be legendary in no time, if u aren't already that is!

Here I will talk about how you should be playing Caitlyn when, and what to do during these times.

Early Game: This is the point in the game where you should just be mostly farming and not trying to crush your opponent(s). Just keep spamming you Q into the minion wave and try to aim it so it hits the minions and maybe catch a champion or two. Then auto attack to get as many last hits as possible. If your opponent is dodging your Q a lot or being really aggressive, either stand back at your tower and farm then, or just go for killing minions. Early game is the most important part for Caitlyn, if you don't farm well enough, you will never be able to do any significant damage early game.

Mid Game: By now first blood should have happened, hopefully caused by you(I mean you killing xD) and you should have at least your boots, your scepter, and a BF Sword. If not, keep farming until you do, if you do, it's time to gank. Caitlyn is not a very good ganker, so you will need to coordinate with your team to get any kills at all. You should already have a kill or two, and the best time to gank is after you kill the opposing mid. Since they will be too distracted to call an mia.

Late Mid Game: By now the laning phase is completely over and skirmishes are happening everywhere you look. You must be a part of as many as you can. Either you evening the fight or making it your teams advantage, you must be trying to kill while still staying safe. If it's a 4v1, don't go and try to help your teammate out. You will die.

Late Game: Now you should be dealing tons of damage and your build should be almost complete. Try to find anybody that's squishy and overextended and BY THEMSELVES to kill, don't go for anything if people are mia. Also, full on team fights are happening and you must be a part of them,keep spamming your Q while trying to go for the squishier characters. If you can't, then aim for whoever your team seems to be focusing until you can.

In this section I am just going to talk about Caitlyn's ultimate, Ace in The Hole. I've played countless games against other Caitlyn's and I want to punch them in the face when they use their ult on me when I have full hp. I can not stress enough that HER ULTIMATE IS NOT AN OPENER. It is strictly a finishing tool and should be used in no other way. With the exception you want to scare somebody from attacking your tower, then go ahead.

Well this is the end of my Caitlyn build. Hope you all liked it! If you didn't , then leave me a comment telling me why. Also, i will be adding more sections later, just have to test a few things out. But if you'd like to see certain sections added sooner just tell me!