I've been using Caitlyn this week, and I just want to know what I could do for a decent build on her. My build hasn't been working too well, because even though the build on paper looks good, it takes too many items to really produce them all. Please help?

Boot + 3 pots
Doran Blade + Vampiric Scepter
Infinity Edge
Phantom Dancer
... (Then adapt to the game)

This is the standard AD Carry build. Works for Grave, Tristana, etc...

What about the Black Cleaver?
I also normally try to get the Bloodthirster, but never really get it.

The only legitimate build is IE PD LW. Caits greatest weakness is low damage. You need to overcome this with you items. Don't get BT, she cant afford to waste money on sustain, especially with her range. Just buy a vamp scepter and don't upgrade it until you are out of item slots.

Black cleaver is actually really strong item, because it doesnt just penetrate armor, it gets rid of it for a period of time, so it makes teammates hit hard. Only problem is, if its the first item your getting, its very hard to have enough AD or enough Attack speed to really fulfill either purposes of the item. At least with people who dont fully understand the role of AD carry. For a while Dignitas's Ad carry CutiePie would start black cleaver every game. And he saw a lot of success.

Heres what I do on every AD carry.

Boots 3 health pots to start, this gives you super strong movement and paired with your range it can be used to autoattack harras really hard, while also giving you decent early game sustain, so you can actually buy something when you go back for the first time.

Doran'sBlade, Normally I get two, unless I'm really fed and can get a BF sword right away. But at least one Dorans blade is a smart idea because it gives you a decent amount of health for the mid game, gives a little bit of damage and also a slight amount of lifesteal to make up for no sustain in your build.

Infinity Edge, the reason you build infinity edge is because with it couples well with the crit chance given by the Attack speed items you'll build later, like Phantom dancer and such. The 250% crits hurt a LOT. BUUUUUT with this being said, in lower levels/elo your farm may not be up to par to get this rather large item, for that I recommend this.

Go by the rule of.. Damage, then Attack speed. Attack speed is better for teamfights, so if you arent having much success and need more damage in fights NOW, then build a BF sword or pickaxe if your really broke, and then build into at least a zeal before you finish this item.