It's not that hard really if you want it to be just a sniper.
High agi, either natural+boosted with Muscle Toner or 'ware arms with high agi ratings.
Decent Str + climbing skills (or athletics skill group) would be nice to get on top of roofs and other good vantage points.
Preferably some intuition for perception dice.
Longarms(Sniper Rifle)
Disguise (Camouflage)
Perception (Visual)
I'm making one right now for a table game. Making him a behind enemy lines scout/sniper/assassination kind of guy, all bioware, only "unalarming" cyberware like 'eyes and ears.
Sniping's really not all that difficult, considering you're only doing a good job when the target is unaware, they don't roll any defense.
Longarms6+Spec2+Agi9+Smartgun2 = 19 dice
8P, -3AP, Load Ex-Ex for 9P, -4AP (APDS if you have 'em)
Take Aim for another +4 dice, you should have time for that as sniper.
Aim for a vulnerable spot, -4 dice, +4 DV
Roll 19 dice, 6 avg hits = 6 net hits (no defense)
Total damage: 9DV+4DV+6Hits = 19 damage, -4 armor.
Should kill most things pretty good.
But like ^ said, most runs sniping just isn't an option.