Hey guys Shanx here with a crazy weird build for you!
Here is a little I'll tell you about me, My online name is Illishanx, I play on the North American server and have been playing since January 2010, I specialize in mid and creating weird crazy builds that work and this is one of those builds, please don't bash it till you try it, thanks!

Another crazy build I made that people loved was Attack damage leblanc go check that out too (hasn't been updated in a while but basically the same idea applies!)

Marks: For Riven I have just found that flat AD seems to be the best since it increases your damage but also increases your survivability off of your shield since it scales off of attack damage, Also, this build is down the utility tree so you need to take AD where you can get it, you can replace these with AD per level since this build is mostly about the late game.
Seals: Health per level seals are runes that I use... ALOT and this build is no exception, Health in my opinion is the best stat in the game, why? because no matter what it is a good stat... since everyone uses it and it is what keeps you alive!
Glyphs: Cooldown is amazing on riven, since she has no mana this will increase her damage and increase her survivability due to her E being up more often!
Quintessences: Same thing here as the Marks, you can switch them to AD per level.

This is mainly where the build differs from others, this is an UTILITY tree Riven page!!! You will probably loose the early game since you are loosing out on health and damage from being utility, BUT late game you will become unstoppable!