According to Mojang, custom block geometry is exclusive to Bedrock Edition. The studio also mentioned that the feature will essentially give players the ability to create any block they can imagine.

Building something in Minecraft can take quite some time. Sometimes, one's block choice doesn't end up being ideal, and players need to swap their blocks for others.

How to get a Command Block Note that only server admins can make Command Blocks. For Minecraft Bedrock Edition, you’ll need to do the following: Enable cheats in your world or Realm settings.