I've been playing Riven alot recently and I have read that people like to get lifesteal items for her. I was wondering, is that really viable? Her attack speed is so slow, I can't imagine that it would do much good, but maybe I'm wrong? I always rush a Phage, then a Frozen Mallet with her as I find the health is more helpful than getting a Wriggles Lantern or whatever.. If the game drags on for a REALLY long time, I might eventually buy a Ravenous Hydra, but I've never tried a lifesteal build.. Any tips or build suggestions you can offer would be appreciated as well.

Stack bloodthirsters. Proceed to carry the game

Riven's abilities scale with AD and Bloodthirster offers the largest amount of flat AD for a low price compared to IE. Likewise, Riven has to auto attack to take advantage of her passive.

BT is core because it gives the most AD for the cheapest price - 100 AD for 3k gold. Riven doesn't need crit chance because most of her damage isn't based off of crit, which is why IE is a poor pickup. It just happens to be the case that BT is the best bang for the buck. Other good options are Black Cleaver and Last Whisper. Black Cleaver should be obvious - she does huge aoe dmg and each hit of her Q will put a stack of BC on the opponents. This not only helps riven do dmg but the rest of the team. LW skyrockets her dmg against tanks.

To give an example of why building defensive items on Riven is bad. I went top against a Riven, she won by a marginal amount vs Darius. She did not build BT or any high dmg attack item but rushed a GA. Because of that she wasn't able to carry the game - her dmg was too low - and I was much more effective than her in team fights. She couldn't kill the carry but I could.

The reason AD is so important on Riven is because all of her abilities scale exceptionally well with AD. Since most of her dmg comes from skills, (even the passive), if her skills/passive don't do a ton of dmg she can't be terribly effective in team fights. So essentially Riven's job in team fights is to jump the squishies after the initiate. She should NOT initiate. Kill squishies and then get blown up is pretty normal.

As for frozen mallet on riven, it is mediocre. It costs more than BT and gives 70 less AD. It gives hp and a slow, but with her mobility slows aren't all that important. If someone can get away from Riven normally they can probably get away even with a slow on (blinkers). So really you get 30 AD and 700 hp for a larger price tag than BT. Not worth it.

Riven procs life steal on her Q, so while you do massive amount of damage you also get health back. (Mistake, see next two posts)
Frozen mallet is an awful item on Riven. She has so much mobility already that the slow is unnecessary. If you want survivability, get a Randiun's Omen. Gives health, armor, passive attack speed slow and active movement speed slow. Absolutely amazing item.

My personal build:
5 pots 2 wards
First back - brutalizer, if you have enough for bf sword get that; pots

Midgame - you are not rushing BC, you are rushing BT. Early brutalizer is just there to give you even more of a lane dominance. Merc treds eventually.
Then get the BC afterwards. More wards/pots

Late game - GA, but the following are situational. Randuin's Omen, that QSS upgrade (CCs are her enemy), LW, Ravenous Hydra, second BT

Final build could be something like:
Merc Treds
Bloodthirster
Black Cleaver
Guardian Angel
Randuin's Omen
Last Whisper

Again many items are situational. Adjust accordingly.

Lol you got me excited there Sho0men. ALL of rivens abilities scale massively off AD, BT gives most AD in game for a cheap price, buy BT as first core item and profit. Not much else to it.