http://gw2skills.net/editor/?vRAQNAo...+jfKBJFg5KtA-e
Here is a quick full build I made, without testing of course.
The idea is to take as less damage as possible and become unstoppable while still doing respectable damage. Are you doing max damage? No. Are you going to stay alive no matter what and revive glass cannon allies in literally one sec so they can do what they do? Yes.
In shroud or reviving you'll have over 3k toughness. While still maintaining 66% chance to crit at all times and a high level of power thanks to deadly strength.
Going in each line blood magic is self explanatory. You revive allies better and teleport them to safety. While also picking up some passive healing to yourself and allies. Since reviving downed allies better needs you to be in shroud it's only complimentary to pick up soul reaping. Death perception vs soul reaping is a personal choice, I'd rather not having shroud skill 4 get interrupted so I like death perception. Strength of the undead gives you a passive damage boost as long as you are above 50% life force. Unyielding blast is required. It's sole purpose is to keep stacks of corrupters fevor up.
Corruptors fevor is self explanatory. More toughness but now we get to the juicy bit which is Dead strength. The more toughness the more damage you will do which is doubled in shroud. This trait single handling keeps your damage up to par since we are getting so much defense. Fevor gives more toughness so you get more power, armored shroud gives you more toughness so you get more power, your runes give you more toughness for more power. It's bread and butter of this build. Putrid defense is the best of the 3 imo and works well with poison cloud.
I think the runes are self explanatory. More revive speed and more toughness.
Off hand can either be dagger or focus, if you pick focus drop poison cloud for well of darkness. If you pick dagger you use dagger 4 to get rid of bleeding and weakness you get from corruption skills. Which in turn activates Fevor for more toughness and power
Protection from wells is weak, it last 3 seconds (it's not per pulse) and if you are full zerker that buff isn't going to help long term or short term. One shot you will still be one shot.
Players will get downed, in an organized group setting though the rest of the team can focus on the boss and designate the necro for revival when that happens. Because the necro won't die from the boss while reviving while other players could get downed with their low defense. So necro becomes the designated reviver in a organized setting.