Welcome to my guide about Caitlyn :)
i recomand u to try this build before voting and after that u can post wadever u lik on this build :)

-Pros
*Able to harrase well
*Able to farm well
*Have a escaping skill
*Have a high dmg skill
*Has a great ulti for killing a kill if not able to reach it

-Cons
*Alot mana needed if skills are usually spammed
*will always get aimed 1st
*very squishy in early game

-Greater Mark of Desolation
This rune is to improve your passive(headshot)dmg in order to harras in early game and to be able to pierce through enemy amrour in early game for easy harrasment

-Greater Seals of Alacrity
This run is to have a better attack spd in the starting so u could farm, harras, get ur passive(headshot) even easier

-Greater Glyph of Strenght
-Greater Qunintessence of strenght
This runes is to make u have greater dmg in early game to have ur pass(heashot) painer and ur early game farming to be easy

I took 24/0/6 cause i noe that Cait is a range carry so u wont realy nid much in the defense because u nid alot of it in the offence such as lifesteal,crit,high dmg output and increase in dmg.
for the utility i put at enchance recall, good hands, swiftness cause of a better way of going back base faster to buy items faster and able to use some extra spd to run back to ur lane fast

I took a Dorans Blade 1st cause cait in the starting is very squishy i the starting and nids a hp item.

I bought BloodThrister because i noe that Cait is a greater farmer and harraser so BloodThrister will increase chance of survivility and killing chances cause of the item's passive and it will also make ur ulti painer than usual
After BloodThirster, i got a Zeal for abit more att sod then i rush for a Infinity Edge for more Crit and Dmg so that my ulti could be painer.

After infinity Edge, i compelete my Zeal to a Phantom Dancer for even better att spd and movement spd, after that i got another Phantom Dancer to be able to shoot even faster and run faster.

After that i will get another BloodThirster for more lifesteal and dmg

Then i sell away my boots to get my 3rd Phantom Dancer in the game to be more faster and more imba >.<

I took flash and exhuast for my Cait

-Flash
it enables u to catch up to people or run away from enemy incase of emergency such as ur piltover is still in cool down

-Exhuast
It enables u to slow the enemy down and reduce armour from the enemy

-Position
try to find a good spot for urself before a teamfight even start so u could shoot then enemys from a distance while ur tanker tank the dmg for u

-Kills
Do not try go for kills in early game unless u r very sure of killing it if not wait until u have ur b.f sword(building infinity the b.fsword)|

-Farm
Try to farm as much as possible for the gold that is needed for ur items

Thats all i have to say, pls vote this guide and this is my 1st time doing a guide so i dun relaly noe u guys will lik it or not :p