Hey, you can add a Box Trigger to your world (Simply search for “Box” in the “Modes” Panel), Resize it like you want to fit the Sector you want.
Then go on the Details panel click on : Blueprint/Add Script. This will create a new blueprint based on this box collision. Inside the blueprint you can select your box collision and go in the Details panel, to the bottom : On begin Overlap.
From the event OnBeginOverlap, Cast the “Other actor” to your player character and Set “Can build” (go to your character blueprint first and create a new variable “CanBuild”).
Hope this helps