Don't be discouraged by groups looking for one particular build or another, try to do your own thing.

Saying that.

Builds are great for getting into a known configuration that allows for your character to be effective in one role or the other.

For your necro there are a few common roles, MM seems to be the most popular, creating minions is easy and they do lots of damage.

There is also the SS build, This involves using Spiteful spirit (elite) to do mass damage on a target and surrounding enemies everytime they do an action. As a MEZ secondry, consider using Arcane Echo to double the damage you can do

The Orders necro has been a fairly popular support build, mostly for IWAY teams and Barrage/Pet teams as Orders give extra damage to physical damage.

More support roles include the Battery build, where the necro uses Blood Is Power or Blood ritual to give an energy boost to team mates.

There are lots of posibilities in this game, I suggest you find something you like and develop it to your own tastes.