PHP Code: 
<g:plusone size="small" href="download.php?id=<?php echo $row->id; ?>"></g:plusone>
Looks good. Small tip.
Replace above with this if you want it to be html5 valid and have consistent root urls. eg all with or without the www part.
PHP Code: 
<div class="g-plusone" data-size="small" data-href="<?php echo WCDDL_PATH; ?>download.php?id=<?php echo $row->id; ?>"></div>