I haven't tried building a theme from scratch, but I have been heavily modifying several themes since I started blogging back in March. In fact most of my css knowledge has been picked up from toying with WP themes.
If you plan on building one completely from the ground up rather than just find a clean theme with a suitable basic layout and chop it up, you will have to learn what a large number of all the template tags do and how they work together.
The best way to do this is probably combining the theory from the official manual/reference at codex.wordpress.org with a whole lot of researching and picking apart the code of at least a few finished themes.
That's the basic content layout covered, you still got a whole lot of headaches ahead of you the actual site layout and style, and depending on your css knowledge and ability to learn from studying premade stylesheets included with other themes that can take a short while or a very long one to learn.
Of course if you are a css wiz and also have a fair amount of coding experience you will likely be able to learn and put together all these things a lot faster than the average webmaster who isn't used to anything much more advanced than building galleries using tables and perhaps a bit of css to style links and borders.
Either way, good luck
. But unless you have very specific needs I would probably still go the route of trying to find a theme suitable for modification instead.
Edit: Just reread your post and noticed you just want to use WP for news. Have you checked out other simpler options instead? Don't know how advanced you need it to be of course, but personally I think I will be going with CuteNews for the news section of my review site.
I'm expecting to try installing it in a couple of days.