This specific design uses a 80mm pattern, just barely fitting into the margins on a US Letter Size sheet.
I really wanted something rectangular, but in principle you could make a square or any other shaped design in Inkscape in a reasonable amount of time. Word on the street is there’s STL-to-Papercraft software too, if you prefer pulp to plastic for everything.
While I was building it, I fed the geometry into DesignSpark just to check on things.
It turns out that my first design, with tabs running all along the top side, probably wouldn’t have worked with my microphone’s shape. Chalk it up to measure twice, cut once!
Now, just pop some graphics on there and print it out! Decent cardstock, a colour printer and exacto knife should do the trick. Or I could laser it, I suppose, though lining things up will be tricky.
Here’s some PDFs if you want to fly with my base design. I’d recommend a rubber band and glue to hold it all together: papercraft_files.zip