private function _findBuildFile($start, $suffix)
    {
        $startf = new PhingFile($start);
        $parent = new PhingFile($startf->getAbsolutePath());
        $file = new PhingFile($parent, $suffix);

        // check if the target file exists in the current directory
        while (!$file->exists()) {
            // change to parent directory
            $parent = $this->_getParentFile($parent);

            // if parent is null, then we are at the root of the fs,
            // complain that we can't find the build file.
            if ($parent === null) {
                throw new ConfigurationException("Could not locate a build file!");
            }
            // refresh our file handle
            $file = new PhingFile($parent, $suffix);
        }

        return $file;
    }