It's fully possible to use Creative Mode to build atop the Nether roof bedrock in Minecraft: Java Edition, but things get trickier when players are doing so in Survival Mode. Moreover, limitations ...

One of the first major looks at Minecraft's overhaul of the Nether biome is available to play on the Java client now.

If you enjoy creating custom worlds for Minecraft, you'll be a big fan of the 20W28A snapshot for Minecraft: Java Edition, which continues adding fixes and improvements to the Nether Update.