with resize tool

LevelMeshEditor.cs

[CustomEditor(typeof(LevelMesh))]
public class LevelMeshEditor : Editor
{
    private int toolBarWidth = 60;
    private int selectedTool;

    private GUIContent selectButton;
    private GUIContent resizeButton;

    private string selectButtonIconPath = "Assets/Resources/Icons/select.png";
    private string resizeButtonIconPath = "Assets/Resources/Icons/resize.png";
    private GUIContent[] toolsButton;

    private void OnEnable()
    {
        Texture2D selectButtonIcon = AssetDatabase.LoadAssetAtPath<Texture2D>(selectButtonIconPath);
        Texture2D resizeButtonicon = AssetDatabase.LoadAssetAtPath<Texture2D>(resizeButtonIconPath);
        
        selectButton = new GUIContent(selectButtonIcon);
        resizeButton = new GUIContent(resizeButtonicon);
        
        toolsButton = new GUIContent[] { selectButton, resizeButton };
    }

    private void OnSceneGUI()
    {
        DrawToolBar(SceneView.lastActiveSceneView);
        DoAction();
    }


    public void DrawToolBar(SceneView view)
    {
        Rect rect = new Rect(0, 0, toolBarWidth, view.position.height);
        GUILayout.BeginArea(rect, EditorStyles.textArea);
        selectedTool = GUILayout.SelectionGrid(selectedTool, toolsButton, 1, EditorStyles.toolbarButton, GUILayout.Width(50), GUILayout.Height(50));
        GUILayout.EndArea();
    }


    private void DoAction()
    {
        switch (selectedTool)
        {
            case 0:
                Select();
                break;
            case 1:
                Resize();
                break;
            default:
                break;
        }
    }

    private void Select() { Debug.Log("I'm selecting something ;)"); }
    private void Resize() { Debug.Log("I'm resizing something ;)"); }
}