Go to "Create Room-Structure-Outside Area" in the left list, and then left-click to draw the outside area. Once the drawing line is enclosed, the outside area is formed. Then you can replace the material of the grassland.
Go to "Create Room-Structure-Outside Area" in the left list, and then left-click to draw the outside area. Once the drawing line is enclosed, the outside area is formed. Then you can replace the material of the grassland.