OH my DaniloDantas... I'm not saying it can't be done but there is a huge support community behind Joomla...
I've spent sometime over the last couple weeks to find something "better than Joomla". Something that doesn't need so much tweaking out of the box, something that once you turn that key doesn't have every option turned on and then makes you spend the next couple wasted hours turning things off and customizing it. Just so I can make a site that may never grow beyond 20 pages or utilized by the client.
Your best bet would be to check a freelance site. Most if not all Members here have little time to do jobs on spec.
I'd strongly suggest that you check all of the options out there before planning to write your own. Many find Drupal superior to Joomla, and there are thousands of others that may already serve your purposes without the months or years dedicated to developing one from scratch.
If you want to start from scratch that can be a bit of a goal beating joomla! But if you are looking to customize something, I would recommend wordpress, believe it or not, it's actually easy to get in there and customize it to be a great cms.
I agree with iggy. I hadn't a clue how to customize WordPress, but once you read a tutorial or two it's quite simple and makes total sense. Last week, I spent Thursday learning what the setup and how to customize a WordPress blog and that Saturday customizing the CSS and such. Now it's awesome. You can look at my final (for now ) product: http://www.chrisdire.com/blog/