Insulation, Radiant and Vapor Barriers - Install attic insulation before ceiling drywall?

I have a new construction detached garage, 16'X22' in size. I am going to finish the garage with drywall and want to insulate it. The ceiling and roof consists of truss construction spaced 24" apart. I would like to insulate the space between the trusses before I hang the ceiling drywall because access is easier. Should I do that or should I wait until the drywall is up? If I can insulate the space before the drywall, how do you hang the batts so it doesn't fall through? Should I use faced or unfaced? I live in mild California climate and the garage will not be used as a living space. Thanks for your expert help.

Having lived in a "mild California climate" before (San Francisco) - I've got to wonder why you want to insulate the garage space since it's going to house cars/stuff rather than people. Assuming you have your own valid reasons, I have to say, it's easier to use faced insulation stapled to the joists prior to drywalling than it is to climb through that small attic access doorway later to roll it/spray it in place.... On the other hand, I've only found faced insulation designed for 16" O.C. rafters rather than 24" (not saying it's not out there, I've just never run across it).....

Just use unfaced insullation! There are these straight pieces of wire they sell in the insulation isle at lowes. If you are on the floor on the ladder insulating looking up, put the insulation between the rafters/joists and put the wire in between the the rafters/joists under the insullation. It will hold the ins. up. The wires will look like a lightly curved "C" as u look up at them w/ the open part of the "C" staring back at you.!! Hard to explain but that is what I would do. If you don't wanna buy those wires which are cheap you can use metal clothes hangers like I have done when I ran out of the original hangers. GOOD LUCK