just play around with yours and ask for a build after 1.1 when they release yet another skill trainer to everyone (only if you have already used the 1st one) who is a sub
there are two "cookie-cutter" builds out there right now but more and more ppl (like me) are trying other stuff

cookie #1: rapid fire - max all the rapid fire skills and mutli+rapid fire everything
cookie #2: +reflected+crit+multi - get minimums in rapid fire tree and then max multishot, max deadeye (for passive crit), max relfected shot, rest in riochet and other skills u feel like
ive read postings on the official forums saying the mm may get some attention in the near future - prolly nerfing reflect and multi and increasing grenade/airstrike usuability so its possible that a good build will have a grenade in there in the future..