Solved Building off the map?

Hi.
What i must change to allow players build on off the map? On flat area.

 

You can already build in the flat area, just not where the spawn locations are (they are designed that way) or outside of the bounds of the map. You can make your own version of the map if you wanted with a larger "flat" area if you'd like, but keep in mind spawn areas are still NoBuildZones.