Lexan panels 2.5mm x 320w x 355h, fastened to the mighty Zortrax by neodymium magnets held in printed ABS grommet/handles. I used 0.2 x 0.5" N42 magnets from K&J Magnetics because I happened to have a bunch of them on hand, but you could adapt other magnets as well:
The gromment is editable on Tinkercad here: https://tinkercad.com/things/gHvDPMyHoH6-magnet-grommet
The magnet hole is slightly undersized and intended to be drilled out with a 5mm bit for a tight press-fit with the magnets. The grommets fit into 1/2" holes drilled into the Lexan with a step bit and can be solvent-welded with MEK or glued with epoxy.
I bought 18 x 24" Lexan panels at Home Depot. To cut Lexan, you should have access to a big metal shear, a table saw with a fine-toothed blade, or a laser cutter; I used a metal shear, which was easy and made a nice edge. If you use acrylic (Plexiglas) you can use the score-and-snap method, but that doesn't work with Lexan.