There are a couple of good reasons to build your own bike, but getting a good deal is not one of them. When a manufacturer is clearing out the previous year's bikes it's amazing what deals you can get.

Some reasons for building your own:
1) You'll learn a lot about how your bike works and gain experience so that you can maintain it yourself.
2) You can hand pic each component to your own preference.
3) You will have a one of a kind bike.
4) You will become emotionally attached to your bike.
5) You will become addicted and spend every spare cent you have on bike stuff.

Seriously, buy a complete bike if you are just getting into it. Find out what you like and don't like about it. Maybe even buy another complete bike the following year. Once you know what type of riding you really want to do and what kind of bike you really want, then you can pick out a sweet frame and build it up.