Reaver: You drop all warrior abilities you had before. You build for damage mitigation and stamina regeneration. You now got 3 abilities you use:
Ring of Pain - uses your stamina, does AoE damage and buffs your other 2 abilities.
Devour - Uses a lot of stamina, and heals you. Heals more the less hp you have.
Dragon Rage - You damage the enemy, but lose health. The lower health, the more damage.
Other 2h warrior build focus on control and knockdowns. Pommel Strike, Grappling Chain, Mighty Blow. It works quite well.
But, let me quote what I wrote on another thread regarding non-specialization 2h warrior/Pre-skyhold warrior:
First of: You start the game with 2 points, you finish the tutorial at level 3. 4 points out of the gate, or 5 as a human. Respec as soon as you can; War cry is not required by a dps.
- First 2 points: Mighty blow + upgrade.
- Second 2 points: Grappling Chain + upgrade.
*This gives you a combo. Grappling chain knocks down, mighty blow deals huge damage to knocked down targets.
- Next 3 points(Level 6, or 5 as human): left side of the 2 handed tree for Pommel Strike.
* Pommel strike: Hits hard. Hits fast. Stuns. Has low CD. Has low Cost. It's awesome.
- Next 2 points(level 8, or 7 as human: Battlemaster tree left side. Pick up Crippling Blows and Combat Roll. At this stage you start seeing lots of Terror demons. You need that roll!
- Next 1 point(Level 9, or 8 as human): Pick up Coupe de Grace in Battlemaster, to the left. More damage on knocked down targets? Awesome!
- Next 2 points(Level 11, or 10 as human): Get Charging Bull in Vanguard. Take War Cry for it. Also upgrade it the next level!
At this point you should be near, or already have, your specialization.
* Note. I know somebody will swear on Charging Bull earlier. If you want to, get it before Coupe de Grace. I woulds till take Pommel strike and Combat roll before it!
This gives you:
Mighty Blow + upgrade: It can knock down multiple targets. It hits hard. It does a shitton of damage on knocked down targets. yey!
Pommel Strike: It hits fast and hard. It cost little, and can be used often. It stuns. It's awesome.
Combat Roll: Evade anything. Mighty blow have a recovery time, at which you can get murdered. With combat roll - just roll out. It cancels the recovery time. It's awesome!
Charging Bull: It serves 3 purposes, or 4 with upgrade: Positional movement, knockdown, guard generator and eventually free-ability.
*Tap
Charging Bull to knock down an enemy, then use a free mighty blow. A lot of damage for 10 stamina

Grappling Chain: Get archers closer. Get mage closer. Knock down stuff. Combo it with Mighty blow for damage, or Pommel strike for CC. Strike. It's pure awesomeness!
Block and Slash: Counter attack. Can avoid a melee attack. If you are tanking 1 melee it's awesome. It's not worth much above that.. but you get it anyways, so might as well use it!
Passives: CD reduction on crit, Weakness on crit and 30% more damage on knockdown or stun (You can do both of these...).
Further on, as a reaver you:
- Get everything in reaver
- Get the defensive passives in Weapon and Shield tree
- Get Combat roll via the right side of Battlemaster.
- Get the stamina passive from Battlemaster(Right side, Deep Reserve)
- Get Charging Bull + upgrade (Tap Charging bull then Devour. Cheap devour!)
As Champion or Templar, just work your way down those tree after you got what I recommended,
Note: This is just my recommendation, so take it as you will 