http://wiki.modxcms.com/index.php/Wayfinder#CSS_Class_Name_Parameters
Example To add one of these parameters to the snippet call use this format: &levelClass=`level`
This will result in <li class="level2">
U could also use the parameter &rowIdPrefix=`true` (havent tried this) and it should give each item a id.
I believe you would create an &outerTpl chunk (which is the outer most container for your nav), and in the chunk, you would have your code:
<ul class="menu">
</ul>
However, you would add:
<ul class="menu"[+wf.classes+]>
[+wf.wrapper+]
</ul>
That should get you started.