level 20
Usually when people are asking about builds, we assume that one is looking for a level 100 char with basically unlimited gear 
If take too much damage, consider getting resistances and some life steal.
Have a look at this 
[1.1.3.1] Budget Lightning DW Ranged Purifier read also the build diary that x1x1x1x2 did, it is linked in the beginning of that thread