You can adjust he measurements for your amp. I would imagine, given how strong this thing is, you could scale it up to a 2x12 combo amp without issues.
My amp has a foot print of 14" x 6.5"
I used what scrap I had laying around so it really cost nothing to make but, you could pick up enough 3/4" birch ply for under $10.
Let's get started!
Step 1: The layout...
I took a framing square and tilted the amp back until I had an angle I liked. In this case it was 2.5" higher at the front edge. I wanted the front of the amp 6" up off the floor at the front as well. So this meant the back would wind up 3.5" from the floor.
Here is the layout on the sides and then the sides cutout.