1st build: Offtank Riven
2nd build: Glassy Riven

Not too much to say, im chilean sorry about my english :P

PD: I repost the build i got some problems the first time...

Here i pick Desolation marks for more damage output at early, Resilence or Evasion seals for more sustentability, Glyphs of Shielding for some MR, and Flat damage Quints to make more easier the last hits :)

In mastries i get offensive maximized and defense as well giving more MR than armor and some evasion... (she dont need mana, etc)

For the items u can pick the offtank for resist and deal nice damage or the glassy one to deal awesome damage vs a poor resistance...
I wont start with Doran's Blade, Riven dont have any heal or regenaration and she need some potions to start laning.

U have to spam E then W and finish with Q in a battle.

I get and
But u can get or with

Pros:

Can easy kill squishies
Not item dependant at early
Can do lots of damage
Have 2 dashes

Cons:

Not really good running
Her dashes are too short
Can't Jungle
At mid game she is item dependant

GL :) and again sorry about my english xD