CAUTION: WALL OF TEXT!
Riven isn't a tanky DPS imo. She does not have any abilities that can really support her "tanky" part, which is why i build her full AD, with AD marks and quints, armor seals, and MR glyphs, as well as 24/3/3 masteries.
By starting with a Doran's Blade, and building another one as soon as you recall, you have early game dominance. This will make your Broken Wings deal about 45 more damage total, your Ki Burst deal another 20 damage, and your Valor give you another 20 health, not to mention the 10 extra damage on every stack of Runic Blade. Comboing Broken Wings and Ki Burst with autoattacks in between = really amazing harass. Last hitting is also not hard, with Valor - just dash in, last hit, Broken Wings out if you must.
After that, you should build Mercury's Treads or Ionian Boots of Lucidity, just because pretty much all other boots are useless on her. She does NOT depend on attack speed at all, or crit damage, just AD. All her skills refresh her autoattack timer, so there is no point in building AS, and crit damage takes away from the damage of your abilities, which is what's important. The Brutalizer is a good item for the transition to mid game, providing a bunch of AD, some armor penetration, and CDR, all of which benefits Riven. It is not necessary to upgrade this to Youmuu's, although sometimes, this is good, but the crit chance isn't needed.
Another item i feel is great for Riven is Sword of the Occult. I have NO idea why nobody uses this. Riven can easily get 10 stacks, and with effort, 20 stacks, resulting in more damage than a Bloodthirster. As long as you play smart, and stack enough AD for your Valor to give you a decent shield, you will be fine with SotO.
By now you should be in mid-endgame. Start building a Bloodthirster or a Last Whisper, depending on your needs - are they stacking armor or are you just ripping them apart, but need more sustain? You could also build the Youmuu's for the active escape. Finally, just build a Frozen Mallet or a Banshee's for a little survivability and a decent passive.
That's just my two cents on Riven's abilities ;P