Inevitably, after a serious workout, you will be sore. Recently I found myself debating with a friend whether or not it was beneficial to massage and stretch your muscles after a good workout in order to help build more muscle mass. Does doing these things help contribute to the process of helping build more muscle, or does it just work out lactic acid buildup.
Thanks.

Stretching before and after any work is an extremely good idea. Your actual workout itself it what builds muscle mass. The stretching and/or massage will basically reduce soreness and/or the possibility of any injuries. I'm sure you are aware that there are different workout techniques you can do if you are wanting to build muscle mass.

I would recommend not doing static stretches before a workout. It's just a bad idea to strain and stress your muscles before you are about to strain and stress your muscles. Its a recipe for injury.

You don't need to stretch before a workout, but if you want to combine stretches with a bit of a warmup, try doing dynamic stretches like skipping, bearwalks, crabwalks, lungewalks, high knees, etc.

You can do static stretching anytime after a workout. It will increase flexibility for sure, and anecdotal evidence suggests it can help strength and muscle gains along with recovery time.

studies have shown that stretching before or after,have no effect on soreness or hypertrophy,if it makes you feel better do it.