Build for ranger? I'd be using launchers primarily. I'm guessing gunner subclass is a nobrainer. I'm not sure if I should get weak bullet or not though, I hear it's really strong.
(gunner tree seems awfully strong. Is that really a x2 modifier to pp generation?)
While I love to use gunner as a sub on most classes to nearly double DPS through throwing out twice as many PA's, it doesn't work too well on launcher. It gets very good PP generation as long as you hit multiple enemies and with the right setup it'll annihilate groups of enemies in one PA meaning PP generation against normal enemies is somewhat meaningless. On the other hand, the PP generation on single targets is abysmal for the launcher and you really wouldn't get much out of doubling it, your passive regen would still outdo it.
A word on standing snipe, it requires you to have been standing still for an entire second before it kicks in, this is problematic with launchers as a fair number of their PA's move your character ever so slightly and since the shots travel slowly, you actually have to stand still until the shot lands, which can be dangerous. You should probably grab Weak Hit Advance instead, launcher shots and most of the PA's will prioritize weak points if they're in line of sight of the explosion and it is easy to get its bonus which is higher than standing snipe's.
Launchers hitting very hard and usually 1-shotting normal enemies, the skill First Hit is very nice to ensure nothing survives by a sliver, forcing you to waste more PP or time.
Power Bullet is nice, it'll buff your R-atk for 30 seconds at the time of loading a special bullet, with 3 different launcher bullet types, that's a pretty nice uptime. PP Save Bullet on the other hand, while it sounds great, is only active while you still have a special shot loaded, which limits its effectiveness, most launcher PA's being somewhat expensive, you wont get to throw out too many before running out of PP and then you're left unable to use normal attacks unless you want to waste your loaded special shots and therefore pp save. I guess it can work if you time the use of the special shots right though and have enough points into them.
Another problem i see with the build is that you invest points in both Ranger's Sharpshooter and gunner Zero Range Advance, which are mutually exclusive, also, the range on Zero Range Advance is extremely short, about 2 character widths if I remember correctly, basically melee range, which may not be very safe with the way the launcher locks you in place temporarily, but you CAN use the launcher in a melee-like fashion with the right PA's.
I have a pure Launcher build too and I do have a single point in weak bullet, I have a crappy low level rifle i use just for WB, load it, shoot it at an existing weak spot, switch back to launcher, make use of Weak hit Advance and deal 9x normal damage. This is the build I use:
http://pso2-skill.pwnedgalaxy.net/skillcalc.php?07dQbsIkbsIkbsIkbsIkbsIkbsIkbsIkfdt0ebIoqnGKJ7JiGA000000ib000000lb2QGFfGFcDeidqbnrA0000lb000009b0000000Ib0000000Ib000000jUltimately, you pick the build that's fun for you though. I enjoy maximizing the damage output of the launcher and playing with a hard-hitting hit-and-run style.