For boots I almost always go with Merc Threads for the tenacity when playing riven. Less time I spend stunned means more change to get away. You can add armor with a wriggles lantern which I almost always buy for the AD, Armor, LifeSteal, and especially (Free ward ever 2 minutes).
So for me,
Boots -> 3 pots -> Merc Threads -> Wriggle's Lantern -> BF Sword -> Blood Thirster -> Phage -> Frozen Mallet(good for slowing in team fights) -> Maw of Malthorius -> Guardian Angel -> Atmas Impaler.
If their team has a lot of ap I might swap out atmas for more MR or build maw before frozen mallet. IF their team is tanky and low on dmg I might rush a last whisperer right after Blood Thirster and leave out GA or Atmas Impaler. IF you have more gold than you can spend (full slots) sell wriggles for something with move speed increase like Force of Nature or a Phantom Dancer or Yomuus Ghostblade (Active ghost).
Attack speed is actually good on riven, just not as beneficial as more AD. Riven's passive does more auto attack damage so hitting faster is good, but mostly for the move speed.
If I'm not soloing top, I take flash and teleport. Me having teleport has saved our game on more than one occasion. I was able to port in on a turret solo 5 v 1 and defend it with Wind Slash, stun, shield, and q'in. I was able to teleport on someone running from their whole team as he was passing some minions I teleported on them, stunned their whole team and flashed out, saved him. Not to mention teleport really helps CS with riven. If solo top though I find that the loss of ignite or exhaust causes me to loose kills.
Riven is really good at saving your team mates lives. The stun is off cd fast at high levels, and your mobility is really good with the q and e combos. Run speed not so great but made up with a ghostblade if your having trouble outrunning the enemy.