2x4's may not be strong enough to support you and your drums, I'd suggest you use 2x6's. More expencive, but probably less expencive than replacing or repairing your drums, not to mention a trip to the emergency room.
Let's pretend that your stage is going to be 8 feet by 8 feet.
Build a square that is 8'x8' (outside measurement)with 2x6' and then place another 2x6 every 16 inches (on center). I prefer using a cordless drill and 3" multi-purpose screws, but common nails and a hammer will suffice, I'm sure. Use 3/4" OSB board for your stage surface.