I'm not sure if you need the cake to be a film reel, or a film reel on a cake, either can be done using the same concept.
For the one I made, I simply dried 2 rounds of gumpaste (cut the holes out and air brushed silver when dry), iced the cake on a board and combed the grooves on top. Place the cake on the lower gumpaste round, wrap a piece of black fondant round the cake, add the white squares, then place on the upper gumpaste round. Everything was secured together with dabs of chocolate so it wouldn't slide.
If you just need a mini reel, I would do the same steps but dry a gumpaste "puck" in place of the cake.