For the main part of it, it is two pieces of fabric, one interfaced, with a piece of felt sandwiched inside. The bottom is the same, with some ribbon sewed onto the top to hide the raw edge. I then pinned the bottom onto the bigger piece (lining the pattern up as much as I could), then I sewed a holding/seam line 1cm in from the edge all the way around. I then sewed ribbon to to hide all the edges, as if it was bias binding.
To create the channels, i sewed from the bottom to the top roughly every 2 cm. Some channels are bigger. I eye balled this. I then just sewed the top over into a flap, holding the top corners down by about an inch. Dead simple. I need to sew some ribbon on to hold it closed.