My version is not exactly how it is in the movie. It's smaller and the inner circles are supposed to connect. It is also supposed to be ~7cm thick. Mine is ~12cm.
Feel free to interpret the measurements.
My interpretation: 25cm diameter, 7cm thick, 7cm ring diameter.
I was limited in foamcore, so I made mine smaller.
Step 1: Materials
-Pic of Lightdisc to copy (Google images)
-Cardboard or Foamcore
-A compass or something round
-Scissors or rasorblade
-Flour and Water