A sniper build doesen't work, compared to a run and gun build.
Problem:
Zombie x has 50 hp
There's to zombie x approaching you
Sniper rifle fires 30 shots/minute, dealing 150 dmg per shot
Automatic rifle fires 600 shots per minute, dealing on average 7,5 dmg per shot
Sniper rifle takes 1 shot to kill a zombie
Automatic rifle takes 7 shots to kill a zombie
Sniper rifle takes 20 seconds to kill 10 zombies
Automatic rifle takes 11 seconds to kill 10 zombies
Thats the state of things. Sniper builds are more or less useless in PvE, except for extremely situational use. But then again, you don't need a sniper build to use a sniper rifle for those situations, so why make a sniper build? Instead, go with something like this:
http://hellgate.ingame.de/charplanner/marksman/?l=50&aa=0&a=00000000&s=0003a010701a00070000000a000Get yourself a pair of Hu's, beacon when needed, phasegrenade will help you phase your targets and finish of pesky packs of fellbores and other low hp mobs that tend to clump up, like zombies summoned by zombie summoners. Build like this, cut cookies.