Okay, so 2 builds for using a crossbow, and one build for just using a bow, and another disagreeing with crossbows.. hmmm
with rapid reload you don't really need a repeating crossbow (unless your going to be using the heavy crossbow of course). since you can reload as a free action. so the money you could spend on that repeating crossbow you could instead put toward a magical crossbow.
Since we raided a ship, I already had in possession a heavy crossbow, and i was planning to get a h. repeating as well when i earned enough, and so far, we haven't come across any magical equipment/weapons so i don't know what are the chances of finding magical crossbow in first local town we go to.
Special considerations
Stabbing Shot - Yes, you have to be an elf, but it rids you of enemies putting you in melee that you can't just 5ft step out of. You could also use Racial Heritage to cheat your way out of the -Con.
Dubious Benefit:
Shot on the Run(and its upgrades) - Again, theoretically it takes you out of melee. Actually it just takes you out of melee reach and into charge range.
Forgot to mention, that most of the people in this dungeon are human, so any other race is disliked, sadly, most of the group isn't human. And, for Shot on the Run, our DM will probably say i would still be in melee if i used a bow/crossbow because I'm highly annoying during the DM's "story time"
I came up with a crossbow sniper build a while back that you may get some mileage out of. It's not as effective as the above rapid fire build, but the looks on your friends' faces when your crossbowman drops two dozen dice on the table for one damage roll will be priceless.
Crossbowman Fighter 7/Sniper Rogue 13
I really love the concept/design of your crossbow sniper but in this dungeon the leveling speed is substantially low(slow) because the idea behind the dungeon was for 4 people, and the last meet up we had 9 people. so the DM has to double/triple the number when we have any encounters, and instead of being possibly what the book says, level 3, we barely just hit level 2. So, if I were to go for this build, it would probably take... forever to see the results or if the dungeon finshes and the DM stops it, I won't be able to see the greatness of it T_T;