sitemap has only source, no design, why?
how shall we outlay it like other page with designer? not only write its code by hand.
Web.sitemap file is merely for having all links properly created. There is no need for its design because you will use this file to be binded with SiteMapDataSource, whcih will be binded with any DataBound control like Menu.
You get the output in the form of navigation on the webpages.
I find there is a not bad tool called "sitemapX" which can auto build sitemap and can check. have a try.