Normally you should play Riven totally on AD ( since all her Spells stack with AD ). But I was just wondering - when I play vs a tanky team with many HP ( Warmogs and stuff ) I usually go for Madred's Bloodrazor when I play AD Carry ( e.g. Ashe ), because of the 4% Dmg from the max. health.
Now my question is - would it be reasonable to go for Madred's Bloodrazor with Riven too? Because normally you wouldn't try to get Rivens Attack Speed up... If no Bloodrazor, what would be another option for her against targets with much HP ?