Well, I had to look it up, but I think that's a wonderful idea. I also made my own out of paving blocks for plants that needed to be up off the ground. I could use a few here, because the ground is so soft, and in the summer, it never dries out. I almost lost my yellow crown of thorns due to rot because its terracotta pot was sitting right on the ground.

I think using staggered size pavers would be a good way to make them. Like take four 24" square pavers for the base, paint them a pretty color, then put four 12" square pavers on those in another pretty color. If you wanted, you could bring it up one more layer with smaller driveway pavers. It would be a lovely way to keep your plants off the ground.

OR you could make your own with poured concrete & boards in any shape and depth you want. Now you've got me thinking!

Home depot sells round heavy cardboard cylindrical forms for pouring concrete into, to make a pillars, posts, etc. You could cut them to the lengths you wanted and get a cheap small concrete mixer frm Craigslist etc. You could even add colorants to your concrete mixes or decorate them other ways.

We used the cardboard forms frm HD to make tunnels for a cat house/tree and glued carpet on it lol. Thats how I know about them.

If you search "concrete block plinth" online and go to images there are all kinds of photos. Sultry, thanks for the tip on the forms. So anyway if you go to a shopping website (maybe even this one) and search for plinth you will find all those fabulous ones made of stone and marble and such, very expensive. This post was also a test to see if anything came up on the right-hand side about a plinth since it appears that this site spies on every word we post on it trying to throw some buying incentives at us. But this time I don't see anything, maybe they are sneakily waiting until I forget about it. LOL!

If you want to make a concrete block plinth like this one pretty, you can always stucco it.

https://www.pinterest.com/pin/420945896394743931/

You can also use PVC pipe as a round mold. It's reusable.

hypertufa immediately comes to mind