As for materials for construction they vary from person to person. I do most all my weapons from wood because that is what I'm good with.
I have seen a lot of sliced constructed weapons done using acrylic sheets and a laser cutter, short of doing castings these have been some of the best weapons I've seen, highly detailed. If you want to do molded ones I'd recommend doing a sliced constructed one as a master.
Slice construction can be done using a scroll saw and 1/4" plywood also.
If you want light weight you can do eva and pvc construction. you can do pretty decent detail with it and foamies
With any method you choose to use to make your weapons take your time do your research and you will get a quality prop you can be proud of.
Squirrelly-ORC (Orsinium Recon Corp)