[2021] expand building area mod?

You can place multiple workbenches at a distance from each other which will increase or expand your build area. The white circle with a dotted outline that you see on the ground will show you the area you can build in.

If you want to use mods, you could e.g. use ValheimPlus with which you can modify the workbench radius. - https://www.nexusmods.com/valheim/mods/4

You're welcome!