I'm going to start building my stage and riser this weekend, and have a quick question for the group.

My riser is going to be 10" high. Am I better off framing the entire riser with 2x10's, or building the outside box with 2x10's, then "hanging" 2x4's like rafters for the balance of the riser? Either way, I'm planning to stuff it with insulation. Just wasn't sure if one method would be preferable to the other. Any feedback would be most welcome. Thanks!

Either way would be fine.
The 2x10s throughout will give you a more solid surface. Or you could do the 2x4 "rafter" system, it depends on how far the distance is your spanning though.
2-3' with 16" centers should be good.