This is my first build post, so please bare with me, and please try it before you knock it. I have had ALOT of 17/1/15 games with this build, and it's alot of fun. It makes a slow champion very fast, and once you get your gear down, you hit like a truck, and thats my play style. It might not be for everybody, but here we go. Keep in mind, Caitlyn, IMHO, cannot mid with this build, she is a rover, she lanes untill about level 4-6 and then starts roaming.

I select All Crit Damage runes because I base this build off of two things, Crit Damage, and Speed. The runes + Infinity Edge = ALOT of damage per shot.

Pros:
-VERY fast early game, you can change lanes quickly for ganks.
-HITS HARD end game.
-Abilities early game make up for her lack of damage from her shots.
-Damage output from shots late game make up for her weak damage from abilities.
-USUALLY the fastest champ on the field end game with this build, exception is Teemo and champs of that likeness.

Cons:
-Very squishy. Dependant on the team I am playing, I will add in health/armour/magic resist to make her survivability a little better, it just depends on how well I am doing, and how well they are doing.
-Does not hit hard midgame. Once you reach level 10, she becomes quite weak with this build. I counter that one of two ways, number one, I will net/trap through team fights and build assists, two, I will farm creeps and neutral mons like there is no tomorrow.
-Very suspect to being ganked. Early Game till level 7, you can meet somebody 1v1 anywhere and eithor kill them or get away, late game you can kill them before they kill you, mid game, if you go 1v1, you're prolly owned.

I use Ghost and Exhaust for two reasons. Attack and Defense.

Attack is obvious, slow them down, get up to them, shoot shoot shoot, hit them with net, shoot shoot shoot, dead. Ghost helps you pursue.

Defense is just as obvious. If you over extend a bit and get caught in a gank, you can exhaust the hard hitting champ trying to kill you, and you can ghost and get out of there, with ghost active, you will be faster then almost EVERYBODY midgame with this build. Master Yi with is ultimate up is the only one so far to catch me.

Piltover Peacemaker is obvious. this ability DECIMATES ALL early game. Non-tanks will lose 1/4 of their health for an indirect hit. By Indirect hit, I mean you shot them through creeps. Keep in mind the damage drops after it hits something first. A clean shot is the way to go if you can, but don't put yourself in the open to be double teamed eithor. Shooting through Creeps will save your life alot. Max this out ASAP, as this will carry you into mid game.

90 Caliber Net is next, this will be your primary need to slow them down to kill them, and oh **** need to get away ability. It has so many uses, You can use it to slow them to kill, you can use it to slow them to get away. The blowback of this ability is VERY useful. It can push you through walls, it can get you away from turrents. At low levels, you can half turrent dive and never get hit by the turrent by simply running up to it with creeps there, fire your piltover peacemaker, then Immediatly, fire your net at the turrent. The turrent will not attack you till your peacemaker hits the enemy, and by then, the net has blown you out far enough, you can get away before it can target you. I have finished off many people with this combo. One of the best in the game IMHO.

Yordle Snap Trap. These are great in lane. Early game, I keep one in each set of bushes to the outside of the lane, as close to the lane as I can get them without them being seen. They serve three purposes there. One: They will go off and show you anybody that was in that bush. Two: They make a great escape route if you get ganked or over extend to much. Three: You can juke an enemy by luring them over the trap, then when it goes up, blow them up. Wonder ability

Ace in the Hole. The range is AMAZING. You can fire it from behind walls, you can start it before they get to the turrent, and if there are creeps on the turrent, they can't run fast enough. At level 6, get them to one bar, let them retreat towards the turrent a bit, pull slightly back like you are letting them go, then turn this ability on them, Death will follow. The reason I fake running away, is their lane partner in the lane sees me back off and dosn't step in the way to help their team mate. By the time the channel is done and they realize what I've done, it's to late to block it.

Headshot. Keep in mind, this charges twice as fast if in brush. I like to try to stay in brush in lanes, 3 shots in, 1 shot out on creeps, then push forward, hit a champ, rinse and repeat. It's a great harrassing tool, and it makes you look like you are hitting harder then you actually are, thus they take pause. Keep in mind, THIS WILL CRIT. With the build I use, at high level, I have had this hit for 1600.

My Item Sequence is simple. Buy boots of speed, and two mana pots and get in lane before they do, push all the way up in the bushes and wait. My lane partner backs up just slightly, cause once they come and I fire my peacemaker, I need to get behind him. I lane with a carry physical melee most of the time. I knock them down in health, get behind them, and shoot away, fire peacemaker at them when it cools down and they die. Simple plan. Pop a mana pot, and start hitting creeps. Keep in mind that there is no mana addition in this build, so conserve your mana.

Usually my first time back, I have enough for my boots of Mobility and my Zeal. Once you have these items, around level 4-5, hit the lane one last time so they think you are still there. Now it's game on. Hit the jungle and river, and go from lane to lane, set up the gank, hit them with a net, if you need to slow, peacemaker ahead of their running space, and hit your ulti when you have it to finish the job if they make it to their turrent, keep on going past mid when they dead to the next lane, rinse and repeat.

Next time back I finish my first phantom dancer, buy my life steal, then buy my agility cloak to start my Infinity Edge build. By this time you should be 3/0/3 or better. At low levels, Caitlyn does not need any help in damage, you should be picking people off left and right. she thrives on kills, this is a VERY expensive build, so if you cannot get the kills early, you cannot build this very easily.

Now comes mid game, team fights start to take place, Finish your infinity edge asap. At this point you are the weakest champ on the field every time untill that item is complete. In team fights, drop your traps right in the middle of the pack, on peoples domes, and fire your net at them if they get to close, shoot, run, shoot, run, shoot, run. Don't forget, you peacemaker is weak now, but fired into a crowd of 4 or 5 champs, it hits every one of them, and every little bit helps your team.

Buy another Zeal.....Depending on how you are doing damage wise to the other team I go one of two routes here. I will eithor finish my Phantom Dancer, or I will finish my Bloodletter. Once your bloodletter is finished, FARM CREEPS. Charge it up, once it's charged, you should be hitting 650 per shot at 1.5 shots per second. You will Life steal almost as quick as they can hurt you. Keep in mind high damage carrys can still eat your life. Hit them, steal some life, half health, hit them with your net, get back, drop a snap trap just in front of you the way you are running, as soon as they step on it, finish them off. If they get wise and run at the last moment, Hit your Ulti on them quickly and they are dead before they know what happened. Keep in mind, at level 18, your ulti will only finish them if they only have a bar or two left. It's just to finish the job. You last item, if the game lasts that long, can be anything to benefit you against the other team. I have had a fed Karthus on the other team at which point my 300 magic bubble from my hexdrinker, and other times they had alot of tanks, somewhere in my build I got some armour pen. The last item always depends on the game.

Like I said at the start, this is my first build, and I have ALOT of fun with this build. I usually que random with my lane partner already so we're use to playing with each other, alot of kills in lane early, and total domination in that lane, once I start to gank, the other team literally starts to rage on /all. I have been called every insult in the book once I start roving because her damage output at low levels is amazing. And Once I get her geared, people look at her as a WEAK late game champ, and I wind up finishing the game with most damage done, highest Crit, and ALOT of kills. Keep in mind, with this build, your team will blame you for KSing them constantly, I just like to remind everybody it's a team game and next time I can let them go 1v1 if they like and they usually shut up. One thing I am good at, if they have their lane under control and we set up the gank, I will net them and let them finish. Don't intentionally KS with Caitlyn, she will do it if you let her, but you wont have a good working relationship with your team mates and it hurts you alot in the long run of the game. Take your assist and move on to the next lane.

Please, I'd love to hear what you guys think, but like I said, don't knock it till you've tried it.