Greeting Summoners,
My name is CrypticRecoil and this is my first build. I have been playing Riven since she came out and wanted to post my personal build. Firstly, Riven is a burst damage champion that focus's on her combos. Secondly, She can dish out a ton of DPS, but she is also very fragile and squishy.

This build focuses on high DPS, with low armor, magic resist, and hp. In this build I do not get any tanky items and focus on dealing the maximum amount of damage in the shortest amount of time.

The runes I choose for Riven are standard for an AD champion.
Greater Mark of Desolation I go with the Armor Penetration Marks for obvious reasons, to shred their armor.
I use Armor Seals to increase Riven's defense, sustain, and survivability. These help in the lower levels.
I use Magic Resist glyphs for the same reason as for the armor seals. They help in the low levels a great deal.
These Cool Down Reduction glyphs are also a decent choice. With more CDR you can use your skills more often which is a major source of your damage combined with Riven's passive.
Greater Quintessence of Desolation These are self explanatory, Major Armor Penetration. These quintessences are made to rip through your enemy.

My explanation for this skill set up is simple:

DAMAGE

This build is focusing on Riven's maximum damage output. When you max Q, you will be hitting a ton of damage. You will then follow it up with your W and stun them. This will allow you to hit and most likely kill them. If not you can try and chase with E, Exhaust, or Flash. In the end they will either flash out or die.

These are my recommended summoner spells:
Flash Flash: Self explanatory, in my personal opinion, it is the best summoner skill in the game. There is a reason why it is the last spell you unlock. Use it well, hop walls, escapes, chases, its just pro!
Exhaust Exhaust: This is a great summoner skill, it slows down the enemy champion so you can deal your damage easier and faster because you don't have to chase him/her. With the exhaust mastery it will also reduce their armor, making you hit harder. And on top of all that good stuff, it also reduces their damage... AMAZING