To simplify a texture-less building 3D model, reduce its polygon count using mesh decimation tools while preserving key structural details (e.g., walls, windows, roof lines).
Use tools like Blender’s Decimate modifier (set to "Collapse" mode for even reduction) or MeshLab’s Quadric Edge Collapse—these remove redundant vertices/faces without distorting the building’s basic shape.
For CAD models (e.g., OBJ/STL), start with a low initial polygon count to smooth simplification. Separate complex parts (like balconies) first to avoid losing small but important features during reduction.