Dodge Tank Assassin[]
Building an assassin to have as high dodge as possible makes a lot of sense...it helps you live longer, dodging further improves your damage, and you already deal crazy amounts of damage thanks to your class perks so you can focus on survivability without too much of a dps loss.
The following build is centered around buffing your dodge chance and HP as high as possible for maximum longevity, leading to a very survivable assassin. Our top priority is to be hit as little as possible and keep up the stacking ATK buff that comes from dodging attacks.
Race[]
Slythin (you'll need to beat Act 1 to unlock it) or Wyspera. Slythins get a whopping 20% bonus chance to dodge when in any of the Close ranges. Wyspera only get a 5% chance to dodge, but this applies at any range. Both also have a small boost to MP regen - Slythin when at Far ranges and Wyspera when repositioning.
Attributes[]
+2 VIT and +2 DEX on each level up.
Mastery[]
Ranged (bow/crossbow) early game, sword/dagger and axe/polearm at late-game. Bows deal bonus damage equal to 30% of our dex, plus we get a 10% bonus to dodge chance while using them. However you can't block when using a bow. Once shields with a >10% blockrate start showing up, switch masteries (and weapons) asap.
Passives[]
Pump HP early on until we hit at least tier 4. After that, armor is our top priority for the extra block rate. ATK is also nice for the extra bleed chance, but armor/hp are most important.
Gearing[]
VIT, DEX, and STR are all important. VIT keeps us alive, STR boosts damage, and DEX does a bit of both...DEX is most important of the 3 but you'll still want a nice mix of stats. Don't worry too much about WIS if you're playing a Slythin (you might want a little for MP regen as any other race) and don't bother with INT at all. Make sure you only use light armor for higher dodge chance. The "umbral" prefix on weapons is extremely useful. On armor, "enraging" or "cloaking" are very useful.
Discipline[]
Shadow. This makes our evasion from DEX increased by 50% which is crucial in this build! The other perk, 20% chance to confuse enemies on reposition (I presume this stacks with the assassin base perk that does the same?) isn't bad either.
Combat[]
Our "primary" rotation is 1 2 3 reposition 3, which takes advantage of the 50% damage boost from reposition for our most powerful attacks and can confuse enemies. Hit confirm whenever you can on bosses to inflict bleed. Don't be afraid to reposition or heal, even if you're sitting on a big combo chain; Better to stay alive than inflict huge damage. Run away from any monster with the "focused" affix as they can't be dodged and you'll be wrecked in a hurry! You might also want to run away from "ranged" enemies if you're playing a Slythin. Luckily we have a good chance to run away thanks to our high DEX.
Once you get >60% dodge and a 30% blockrate shield, you're nearly unkillable and should just breeze through any encounter. Good luck!