This is not hard!
Materials:
-5 mm aluminum.
-Plywood (I recommend thicker plywood on the back than front side of the wheel)
-Paint according to taste (recommend water based because of the thinner based top coat)
-Gel Coat or Epoxy top coat.
I did all aluminum cutting with grinder and drill. If you have access to a laser cutter og similar, that would of course be much better.