As world type FLAT does not seem to do this, is there any way to generate a plain, flat world?
You do that by going to your world's world.ini and changing the values in [Generator] to:
Code:
BiomeGen=Constant
ConstantBiome=Plains
HeightGen=Flat
FlatHeight=5
CompositionGen=Classic
ClassicSeaLevel=0
ClassicBeachHeight=-1
Finishers=
Thank you so much!!

This doesn't work with the current version of cuberite. The world is around 60 blocks height and not completely flat and there are small hills.
Try to set the ShapeGen to "HeightMap"
Had to add also SeaLevel=0, then it works fine
