Hello! I think it's a little hard to build your own flatland world. It's annoying how you have to look up a code to build your own custom flatland. I think it should be easier. How about putting in, let's say, a bar like this:
But with another line closing it, making it a rectangle. Then, you have an arrow on the right side on the box. You click anywhere in the box, and then you could choose any block, and for each block you choose, it will add one more layer to your flatland. And also, there would be a few boxes below it. Maybe one would say villages, one of then dungeons, abandoned mine shafts, mineral spawning, and so on. This way, you don't have to look up a code to make one or ask your friend to help you. If this is applied, EVERYONE will be able to make any flatland world they want, and it would also make map making easier.