I love making purses. I definitely would buy a pattern to make your first one. I have bought several patterns - like to get them at Joanne's when they have the 99cent patterns. Another wonderful (but more expensive patterns but they are awesome) is
http://www.studiokatdesigns.com/
Here is a link for links to many free patterns.
http://www.henriettashandbags.com/Craft_Ideas.html)