I once made one out of Oak that was cut from the yard, air dried for a year or so and milled it when I had my shop in the basement. But I guess it wasn't well acclimatized to the shop when I glued and milled the boards. Or maybe the wood just was not dry enough and it warped. I never installed it, nor made the second one.
Finally yesterday I started new ones. Having leftover 5mm MDF from a previous project, thats what was selected as it gets a few coats of paint anyway. I cut two panels at the same size and used double-sided tape to stick the panels together so I could work on them at one.
With a straight flute router bit/ cutter and the router on a guide rail the flutes were routed. Pencil marks on the guide rail marked the beginning and endings of the two row flutes to be routed.

To anyways keep good sight at the router bit and the markings on the panels I decided not to connect the dust collecting hood and vacuum. Instead I vacuumed after each cut.
Detail of the finished cut flutes on the two panels. Notice I crossed my pencil lines. This was done intensionally as I figured it is more pleasing to the eye.
To make a frame for the panels Pine was ripped in half on the table saw and went through the thickness planer. Here miter joints are cut on the miter saw.
Glued mitered frame in clamps drying. Initially I just used paper tape as "clamps" but while I was doing this I looked to my right and saw a couple of clamps and though... Yeah, well...
The MDF panels in their Pine frames ready for some primer paint.
In the primer...
And here dried with a second coat of grey paint.
Here it is installed on the first floor.
And here on the second floor.