I'm not sure if this would be the classfield for this but i'm sorry if it isn't... But, how would I make a super flat world that isn't just 3 blocks thick? I want something like 40 blocks at least thick or more.
Make a new world, make it Superflat, go to customize, click Presets, it will say 2:7,2x3 and so on. change the 2 in the 2x3 to any number you want, and that is how thick it will be.
You can also use one of the presets that are already there for you, such as the Overworld preset, which will give you most of the stuff you normally get in a normal world, except for only one biome and no caves.
TheMasterCaver's First World - possibly the most caved-out world in Minecraft history - includes world download.
TheMasterCaver's World - my own version of Minecraft largely based on my views of how the game should have evolved since 1.6.4.
Why do I still play in 1.6.4?