I said I'd do this a long time ago, and never got around to it so here it goes.
There are many reasons to build a riser for the drum kit.
Comfort - Raising the drums up off of a cold concrete floor will help, as well as afford a place to put the spikes out so the drums won't slide around!
Sound quality - drums up on an isolated riser sound tighter because the riser doesn't eat up the low frequencies that travel through the floor
I made my drum riser by assebling a frame out of 2x4's, wood glue, and screws. I used premium lumber, not that fingerjointed stud material. Those things are meant to handle vertical, not horizontal pressure and can come apart!
It didn't take much lumber to make my drum riser - 6'x8', with a tapered front.
If you aren't handy like I am, here's a hint: drilling pilot holes in one side of the wood prevents bridging which is when the threads of the screws prevent the pieces from coming together tightly.
After I added the plywood decking [with screws and wood glue] I routed the edge flush with the 2x4's.
I brought it inside [HEAVY] and put some rigid insulation I had cut for me! Insulated so that the riser doesn't turn into a giant speaker. The insualtion I used was 3" thick and fit very tightly.
After that I drilled pilot holes in some hockey pucks to isolate the riser from the floor and screwed them in!
Then, I added some 3" felt furniture pads to the hockey pucks to protect my hardwood floors.
I completed the drum riser a long time ago. Between now and then I added 2 light fixtures with LED bulbs that change colours [just for fun while jamming] and put on some temporary carpets. I'm looking for a specific pattern of carpet but unfortunately I am told that it is hard to find... I'm on the lookout!