Started by making a design ( in Designspark Mechanical ):

Since I found some pieces of 8 and 12mm MDF in my shed, these are the only ones I use.

Now I don't own a sophisticated workshop, and I don't have one of these fancy table-saws that woodworking YouTubers always seem to have. But last year I renovated our stairs and decided to buy a 'track saw', which actually works very nice and allows for some really nice straight cuts.

Next will be the assembly.