This is my first build so things might be off, however i am a regular riven player and have always done well with this build.
For this build you need to play aggressive early to assertive good lane dominance however you always need to be careful from junglers as they can ruin everything for you if you play to cocky.

I use a mix between Armor, cool downs and damage as riven needs to be strong early to push the enemy out of lane.
However i do also recommend MR glyphs instead of cool down as this gives more defense especially if against an AP top or jungle.

Good early game items with a mix of defense with damage. Builds into Good late/mid game items also.
Black cleaver can always be subbed out for anything else in the late game also the wriggles can always be change towards later game.
Alternatives could be Warmogs, Sun fire cape, Bloodthirster etc...

I like the flash for offensive and defensive uses also Teleport is very useful for top laners and can help alot if other lane are getting pushed and you can help.

Pros
Very mobile
Good stun and knock back
Quite strong as Offtank

Cons
Easily kited
Once enemy has edge, its hard to fight back
Can be difficult to play

A good mix of Q and W can clean waves out fast especially with boost on AD when using this, Do not be afraid to use spells to clear waves and cool downs are quite short.