The good thing about this, is that you can lay breeze blocks, or any concrete block - even brick, in a dry state, and if you want to change it all, you can take them all up and start all over again!
I love the concept of dry-stone walling, and using blocks is only another way to build something! I have some really heavy concrete blocks holding up our bean bed here (we're on a slope), and they've been there for years! The mint grows through them and they get covered with 'Mind-your-own-business' leaves, and we love it all! They never move, (but they are darned heavy)!
Concrete blocks are inert, easy to brush off, and while they may look a bit 'ugly' at first, so what! They're cheaper than wooden sleepers, and much more versatile! Maybe try some 'L' shapes, or even a semi-circle so you have lots of holes etc.! Hanging plants like lobelia love them too! And, you can plant stuff right up next to them so it's a no-brainer!
So there's my take on a great idea you have!
(I may even try another similar idea here, but give me time...:0~)