Welcome to my riven build.
Riven i have found to be a very powerful Champion when used correctly.
This build is focused on some early game survivability while building up your attack damage items.

With runes as i have mentioned i build for early survivability due to the fact that my team normally builds melee champions.
So you could change the armor and magic resist for damage, crit chance or speed.
Crit can be useful and i don't believe you will need a lot of speed.

Masteries i think are obvious 21/1/8
High damage with less time dead plus xp increase is my personal choice which i believe works well.
i placed one point onto armor cause i don't really care much for crit on my build but you may do so.

I start off with a long sword and health pot to give me early game damage and lane staying power. If need be i may go back and grab some extra pots.

i then build into a brutalizer and phage looking to build into a ghost blade and frozen mallet for mid to late game.
Frozen mallet is always in my build for its health and slow effects which help me survive late game. (before this i was getting squished)
Ghost blade is also a main part of my build for its att power, pen and speed buff it grants allowing me to enter a team fight fast and furiously.

Hexdrinker is a situational item and is bought if there are some heavy spell users on the other team.
Last whisper and infinity edge are some nice attack power items which can rip through armor.

I may switch hexdrinker, last whisper and infinity edge with different items depending on the situation. Say building thorn mail when a team may have some crazy AD carries.

I tend not to like bloodthirstier due to them being a snowball item but they can have their place. Trinity force is another item that may be useful due to the sheen effect and attack speed.

Finale thought, boots.
garbing boots of lucidity is a good choice for CDR but grab mercury treads if there is a lot of stuns on the other team.

Black cleaver is an item i recommend not getting for riven since she isn't a auto attacking champion.

I try to keep valor for escapes but it is good for entering a fight and absorbing the first hit or so.
Use broken wings, auto attack, ki burst, auto attack, broken wings, auto attack then try to land the finale broken wings in front of your opponent forcing them backwards.
the auto attack is important due to riven passive which increases her damage after every use of a skill up to a max stack of 3.

This is why attack speed is viable for riven to land those extra attacks in mid combo.

In lane i try to harass as much as possible until lv6 when i get my ultimate allowing me to go in for the kill.
i grab ki burst over the other skills since it has some nice damage output and is a stun. I will sometime harass by using valor to enter and then using ki burst to deal some damamge and stun before leaving.(you can use broken wings to get out faster if you wish)

When using broken wins on a opponent especially on someone that is fleeing try to land the final Q hit in-front of them to knock them backwards into your team. Also by maxing ki burst first you can chase down champions and constantly stun them.

Your stun can also be used to save your team mates due to the fact that riven can move in and out very well so if you see the chance to save someone get close to the chasing champ and use ki burst then valor and broken wings to escape.

By mid late game you should be entering every team fight with your ulti on (this does not mean every fight just every team fight) Also it is a good idea to activate ghost blade as well at this point.
Any champions that try to leave the fight due to low health can be finished of with a wind blade. The reason i say enter every fight with your ulti on is cause it only has a 30 sec cool down or less (depending on builds).

Pros
*some survivability early game
*good damage output and finisher
*mobility
*great stun
*good chaser
*great harass

Cons
*Silences and stuns can ruin your combo so watch other champions and wait for the right time
*even tho you may have some survivability in late game you will go squish so wait for tanks and other tanky dps to go in first.

Riven is a mobile harass machine, early on harass your opponents with valor and ki burst using broken wings to get out or using broken wings to get in ki burst then use valor to get out.

Save team mates when you can by using ki burst along side valor and broken wings.

Use your ulti in every team fight for its 20% damage increase

Stuns, silences and slows will ruin your day.

Don't charge in first wait for someone that is more tanky to go in first.

This is my first time doing a build guide but i thought it could help me think about my own build and get the help of the community to improve this build.
Thank you