Amazing Robkk! It is exactly what I was looking for!
<?php if ( get_current_user_id() == bbp_get_topic_author_id() ) : ?>
<?php bbp_get_template_part( 'form', 'reply' ); ?>
<?php elseif ( current_user_can( 'moderate' ) ) : ?>
<?php bbp_get_template_part( 'form', 'reply' ); ?>
<?php else : ?>
<div class="bbp-template-notice">
<p><?php _e( 'You do not have permission to reply to this topic.', 'bbpress' ); ?></p>
</div>
<?php endif; ?>
Thanks a lot!