I have the same "todo" and as I will replace the trunk floor prolly somewhere end of this year I'll have to make mine too.
I have already thought about it and bought 1.5mm sheet for that.
There's no rocket science involved to fab them, aside ensuring you are cutting the metal straight for a good look,
the tricky part is only the second fold. So if of any help, may you'd go for it, here's how i plan to make mine... I'd look or buy for a piece of metal that is as thick as the space between two folds and wide as the space between the two side. A piece of hard oak wood would do the trick too if you can't find a piece of metal.
Once you have your "star" cut flat and your holes for the spot welds done. You can put that metal in a vice with your "star" or (using a metal breaker) make both first 90 deg folds.
The help metal then squeezed/clamped between the two, you can then with a piece of wood push them toward center and finish the last degrees with a hammer. (That's where having a metal piece behind would help to get a sharp line). The edge of the block acting as a metal breaker.
Here a quick view of my "plan"
Where, in green is an extra length, that will help to push in the second fold and help correct visually any misalignment after it's folded . Disc/cut after each of the too folds.
Hope it helps