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

I just found this out with valheim+. thank you for the response.

You're welcome!

in case u didn't realize it yet, the added workbenches don't need to be accessible to expand ur radius. No roof or walls, just build it & go.