: Use the Flattery or Unwrap extension to lay the building's walls and roof flat on the ground plane.
With a proper Point Link workflow:
The becomes exponentially more difficult when you use Groups and Components—which you should always use. A point inside a group is blind to a point outside the group. sketchup building point link
To manually "link" points to form a building’s structure, you use the : Clicking one endpoint and then another creates an edge. : Use the Flattery or Unwrap extension to
: A similar alternative for creating flat faces from 3D objects, often used for complex or non-box shapes. sketchup building point link