Were I you, I would start with Django so that I would have an application up and running faster. And then, since Django is open source, start poking around at the internals to see how it works.

I would wait to roll your own web framework until you've had a little more programming time under your belt. Regardless of whether you may be a quick study or not, rolling your own framework is going to have all sorts of strange issues come up, and sometimes it's nice to be able to ask around on a forum, mailing list or IRC for help. Django has one of the largest (if not _the_ largest) Python community; at least as far as currently common frameworks go.

Django is quite nice as a framework as well, it may turn out that it's all you ever need. There are quite a few people out there who use it for every project they work on, with great results.

[Edit: Changed "webapp" to read "web framework"]