While Tiko build plate works well, I like having multiple build plates and don't like printing with rafts.
These rings help keep the Tiko from shifting when placed on a glass or polycarbonate sheet, and act as a template for cutting the sheet. Just glue the ring on a sheet of polycarbonate, then trim the edges with a 3d printed router table.
I used 1/8" polycarbonate (these were left over from my RigidBot), but thinner sheets would be cheaper and probably would work just as well. The sheets should be about 10" square or larger.