def METHOD_NAME(self, start_dir):
    """ Figure out the base dir (where the top-level cmake file is) """
    base_dir = os.path.abspath(start_dir)
    if self._check_directory(base_dir):
        return base_dir
    else:
        (up_dir, this_dir) = os.path.split(base_dir)
        if os.path.split(up_dir)[1] == 'include':
            up_dir = os.path.split(up_dir)[0]
        if self._check_directory(up_dir):
            return up_dir
    return None