Honestly a solid pistol route would be best for soloing. You can't always snipe in single player, especially in ambush situations. A fast shooting repeater for close range combat or a solid revolver for medium range combat gives you a lot more flexibility.
I'd stick with that until level 25 or so when you can cap off a skill tree, then change over to either the bird tree or the snipe tree.
"No, whats an STD? Is it a new instance or something!??!?1/1" atfxkmk
Max the Rogue tree first, followed by the crit bonus from the gunslinger tree, then the rest. This build focuses on snipers and revolvers for headshots, rather than repeaters. Anything Bloodwing doesn't kill is dazed, making for easy headshots. If you can't get headshots/crits easily, you may want to go for something more gunslinger focused and use repeaters instead.
There really isn't much else worth getting in the Gunslinger tree. For Bloodwing builds, Carrion Call is infinitely better than Predator, for cooldown. With maxed Carrion Call and a sniper rifle with a decent ROF, you can often have Bloodwing ready to go again before he returns from doing his 6 hits. You can swap Focus for Killer if you're comfortable with your accuracy/sway.
Also, don't underestimate the power of a high fire multiplier/chance to effect. Up until level 40 or so, I used a high DOT sniper over snipers with twice the damage, because the DOT was just too good (especially the Volcano snipers with red text "Pele Demands A Sacrifice!").
I made a damn good build for myself and I wouldn't change it for anything in the world. This game is no where near as complex as most RPG games. Making a build is easy as pie. If it adds to your damage, reload speed or fire rate than it's good. Anyways, here is what I did, feel free to substitute whatever you'd like with whatever.