Hello. This is the first guide I'v ever made so please feel free to criticize it all you want.
For starters Riven is not in any way a tank, she is a fighter(bruiser) which means she can be beefy but will not suffice for a proper tank. She has no abilities that scale with AP in any way so not building a Trinity force would be the way to go.

Runes are cruicial to survivability with my build.
I use 9 greater marks of desolation(armour penetration), 9 Greater seals of ressiliance(armour),
9 greater glyphs of warding(magic resistance), and 3 quints of desolation(armour penetration).

The reason for all the ARP i take is beause I don't get too much AS till later on in the game, most of my items give me tons of AD early on which makes those ARP runes much more useful then AS runes.

I take the armour seals and magic resist glyphs for my survivability, I find her to be very squishy otherwise.

Doran's blade seems to be the best choice for s starting item, you get AD, health, and lifestealing, I then make my berserker greaves so that my passive is being used and not being wasted, otherwise I would take boots of swiftness.
I create a bloodthirster first so I can have a large amount of AD and having that 25% lifestealing(15% without full stacks) really makes lanein easier, you don't need to recall after every fight and you usually get the upper hand in the fights.
After that I build a Last whisper for more AD and ARP, the more ARP I have the more damage I'm gonna be doing, at this point yur openent armour should mean nothing.
I then work my way into an infinities edge to give my AD a real boost, with this you shouldn't have a problem doing 1v1 against a non-fed openent, the more squishy champions should die almost instantly.
Phantom dancer is up next giving me crit rating movement speed and the AS weve been needing, after this is finished ur passive should be stacked as much as you can because your gonna blow those stacks away fast.
Finaly I build The Black Cleaver, this item should iltimatly make a you a tank killer, you should have enogh AS to put 3 stacks up almost instantly and top it off with your last whisper and it should seem like the oponents have no armour.

If I enter a 1v1 or a 2v2 I use broken wings 3 times instantly for the knockback giving your teammate or yourself a chance for an extra hit that the oponent doesn't get, I then instantly use my valor for the shield to soak a hit or 2, after that I use Ki burst, after your Ki burst is used your broken wings should be off CD or a few seconds off, after that just repeat.

If you need to run from an enemy and they are chasing you start off by using valor to get a short distance ahead, then use your broken wings 3 times very fast to get another small distance away and if u repat this combo you shouldn't have much of a problem running depending on the champion your running from. If the champion thats chasing you is very hard to run from try to find a wall and flash over it to ultimatley save your life.

I take on a basic offensive tree, the armour and magic resist talents under defensive, and the reduced time while dead under utility 21/6/3.

I take the armour and magic resist talents under the defensive tree so that my survivability along with the runes will be much higher.

and the last 3 points I just put the in the reduced time while dead is so that I have more playtime.