to make a robe, you really don't need any sewing talent at all. I know this isn't a harry potter robe, but this would give you the basic idea of making a robe:
http://www.padawansguide.com/robe.shtml
the only difference is the hood, depending on the film, you probably want to come to a point rather than round off and I doubt you'd want the sleeves as large. Other than that the lining is house colored material. But, if you're not even wanting to cut your teeth...looks like some people have already found some good options for yah. Good luck with your search!