Level the cakes and cut each one in half so you have four layers.
Using a 5" cookie cutter cut a hole in the centre of 3 of the cakes and leave them to one side.
Place your first cake (one with the centre missing) onto your cake board/serving plate. Pipe the orange buttercream around the edge of the cake, then pipe the green next to it, then purple moving closer to the centre of the cake.
Stack the next two cakes (ones with the centres missing)with the same technique.
Fill the centre of your cake with your chocolates and sweets. Once it is completely full put your final cake on top.
Pipe or spread the green buttercream around the bottom of the cake. Spread or pipe the purple in the middle and the orange on the top of the cake.
Using your smoother, smooth around the sides, if there are any gaps fill these with the buttercream and continue to smooth around the sides until the cake is smooth. You will most likely take some of the buttercream off the cake if you do pop this back into your bowl.
To smooth the top edges of the cake, use a palette knife and smooth any buttercream into the top of the cake.
Leave the cake to one side.