Not much to say about her really. She's strong like all heroes but the nice thing about Riven is that she really need a good reflex to master. Because of this when I dominate a game with Riven I'm always happy that I got to be that great because I know how to execute a perfect skill sequence and not just use my auto attack.

I would also like to note here that I am by no means claiming that this is the best build or way to play Riven. By time of writing I'm not level 30 (I'm 26) and I have never played a ranked game with her so it might not work so well in some cases.

(I will also apologize for all my spellings mistakes up front for now)

I published this guide by accident now while it wasn't complete. Just enjoy the part thats already there. I will be adding more in the future

Greater Mark of Desolation: You will need this. The AP it provides is just really really great. Against a tank focusing on armor it will help to lower that. Combined with Youmuu's Ghostblade and Greater Quintessence of Desolation this will give you enough AP to slice through just about anyone. If they really focus on armor because you are the main damage dealer of because you have to much AD on your team you should pick up Black Cleaver

Greater Seal of Armor: You take this with you for early game durability. This will give you just enough armor to survive the early game ganks and it enables you to stay in lane longer early game.

Greater Glyph of Magic Resist: Actually same as above but this is against those pesky casters.

Greater Quintessence of Desolation: See above :)

Riven fight's melee and has no mana. This build is all about dealing the most damage in the lowest time and so that if you die you get back quickly.
I tried playing Riven with a utility build but it just doesn't work for me. If you don't go for a full attack build she lacks the early game killing power which i love about her.

You leave HQ with Doran's Blade. This will give you the health to initiate the first attack with your lane partner, it gives you additional damage for the early early game and the live steal makes sure you can stay in lane.
If you can stay in lane long enough to get enough gold for Wriggle's Lantern pick that up before the Boots. Riven's skills should be quick enough to catch up or to flee in the early game. Plus if you get Wriggle's Lantern quickly you can ward the bushes against ganks. Wriggle's Lantern will be the main source of your life in practicly the whole game. If you can't get the kill with that attack just back down and life steal yourself back up and then do it all again.

Berserker's Greaves are here because we want to attack beween each of our skills. (more on that later) If your auto attack is to slow you won't be using Riven to the maximum.
Once you arrive this far you should be able to stay in lane, harras enemies without getting much damage back and you will be able to see ganks coming. Now it's time to build some damage. Because Riven focuses so much on the skill - auto attack - skill combination it's not really usefull to have to much attack speed.
Infinity Edge is perfect for this it give a lot of attack damage for your skills and it also gives you this nice little critical strike which really hurts in between your skill attacks.

As I already explained in the runes part to get the additional AP you need you will need Youmuu's Ghostblade or Black Cleaver. If someone else already has Black Cleaver don't make it. Then just go for Youmuu's Ghostblade. If you have Youmuu's Ghostblade don't forget to use the active ability when you get into a teamfight.

Bloodthirster More damage and more life steal. This will increase your damage and combined with Wriggle's Lantern the total amount of lifesteal you have is ridiculous.

Guardian Angel This is purely there to finish everything. You should be strong enough to kill everything and this just adds to your durability. Also because of this nice little passive you will be able to finish a teamfight even if they focus on you first.
If the enemy team doesn't focus you or if you think you still don't deal enough damage you can always go for Phantom Dancer. I don't think this is really necessary because your skills are your main damage and not your auto attack but it gives a nice extra critical chance.