In order to build an empty room in Bloxburg, you will need:
-A walls tool
-A flooring tool
-A roofing tool
Once you have these three tools, you can then begin to build your empty room. To do so, simply select the walls tool and click and drag to create your desired room shape. Then, use the flooring tool to add a floor to your room. Finally, use the roofing tool to add a roof.
And that's it! Once you have these three tools, you can easily build an empty room in Bloxburg.