public class ExampleClass : MonoBehaviour
{
    public LODGroup group;

    void Start()
    {
        // Programmatically create a LOD group and add LOD levels.
        // Create a GUI that allows for forcing a specific LOD level.
        group = gameObject.AddComponent<LODGroup>();

        // Add 4 LOD levels
        LOD[] lods = new LOD[4];
        for (int i = 0; i < 4; i++)
        {
            PrimitiveType primType = PrimitiveType.Cube;
            switch (i)
            {
                case 1:
                    primType = PrimitiveType.Capsule;
                    break;
                case 2:
                    primType = PrimitiveType.Sphere;
                    break;
                case 3:
                    primType = PrimitiveType.Cylinder;
                    break;
            }
            GameObject go = GameObject.CreatePrimitive(primType);
            go.transform.parent = gameObject.transform;
            Renderer[] renderers = new Renderer[1];
            renderers[0] = go.GetComponent<Renderer>();
            lods[i] = new LOD(1.0F / (i + 1), renderers);
        }
        group.SetLODs(lods);
        group.RecalculateBounds();
    }

    void OnGUI()
    {
        if (GUILayout.Button("Enable / Disable"))
            group.enabled = !group.enabled;

        if (GUILayout.Button("Default"))
            group.ForceLOD(-1);

        if (GUILayout.Button("Force 0"))
            group.ForceLOD(0);

        if (GUILayout.Button("Force 1"))
            group.ForceLOD(1);

        if (GUILayout.Button("Force 2"))
            group.ForceLOD(2);

        if (GUILayout.Button("Force 3"))
            group.ForceLOD(3);

        if (GUILayout.Button("Force 4"))
            group.ForceLOD(4);

        if (GUILayout.Button("Force 5"))
            group.ForceLOD(5);

        if (GUILayout.Button("Force 6"))
            group.ForceLOD(6);
    }
}