void OnBuildTrainingGroundButtonButtonClicked()
    {
        build_panel.SetActive(false);
        GameObject build_helper = GameObject.Find("BuildHelper");

        if (build_helper)
        {
            BuildHelper helper = build_helper.GetComponent <BuildHelper>();
            helper.EnableBuildMode(training_ground_prefab);
        }
    }
    void OnBuildCanteenButtonClicked()
    {
        build_panel.SetActive(false);
        GameObject build_helper = GameObject.Find("BuildHelper");

        if (build_helper)
        {
            BuildHelper helper = build_helper.GetComponent <BuildHelper>();
            helper.EnableBuildMode(canteen_prefab);
        }
    }