the materials list is a foldout. Click on it and there will be a list where you are able to add a material which changes it visually. The physic material property takes in a physic material. I cam sent a short clip in a few hours.
EDIT:
I've tested it with 2018.4 and there are some names that are different so there are a few manuell steps you need to follow:
1. Remove all [SerializeReference] attribtues in RoadCreator and Intersection
2. Change DrawPositionHandle in the Utility class to the following:
public static Vector3 DrawPositionHandle(float handleSize, Vector3 position, Quaternion rotation) { Color color = Handles.color; Handles.color = Handles.xAxisColor; position = Handles.Slider(position, rotation * Vector3.right, handleSize, Handles.ArrowHandleCap, EditorPrefs.GetFloat("MoveSnapX")); Handles.color = Handles.yAxisColor; position = Handles.Slider(position, rotation * Vector3.up, handleSize, Handles.ArrowHandleCap, EditorPrefs.GetFloat("MoveSnapY")); Handles.color = Handles.zAxisColor; position = Handles.Slider(position, rotation * Vector3.forward, handleSize, Handles.ArrowHandleCap, EditorPrefs.GetFloat("MoveSnapZ")); Handles.color = Handles.centerColor; position = Handles.FreeMoveHandle(position, rotation, handleSize * 0.15f, new Vector3(EditorPrefs.GetFloat("MoveSnapX"), EditorPrefs.GetFloat("MoveSnapY"), EditorPrefs.GetFloat("MoveSnapZ")), Handles.RectangleHandleCap); Handles.color = color; return position; }
3. Change SceneView.duringSceneGui += OnSceneGUI; to SceneView.onSceneGUIDelegate += OnSceneGUI; in ContextClickSelect constructor.
There is one more steps but I'll upload a update with that in a few hours which fixing you not being able to open the material foldout. If you want to fix it now then change EditorGUILayout.PropertyField(serializedObject.FindProperty("lanes").GetArrayElementAtIndex(tab).FindPropertyRelative("materials"));
to EditorGUILayout.PropertyField(serializedObject.FindProperty("lanes").GetArrayElementAtIndex(tab).FindPropertyRelative("materials"), true); in RoadEditor.
I'm sorry that you have to change things manually but as Unity changes names I can't create a version that automatically works for both and these changes should only take like a minute with Find And Replace.
EDIT 2: The update has now been posted so if you download it and also follow the instructions above the tools should work in your Unity version.