Ever hated to break blocks just to create a flat space? I had that feeling too so I searched for flat Minecraft worlds and I came up with this! http://www.minecraftforum.net/viewtopic.php?f=1020&t=121930 check it out.
I built a Rollercoaster on that map. but you have to use third party software to fill your inventory since no trees, ores, or anything used for building stuff wont spawn. Although the flat world is big it is not infinite. It's 1024x1024x128 Blocks and has a bedrock wall. The normal world is made flat but the Nether isnt. So you can all have fun now with the flat Minecraft world!!
