I don't recommend building your own content management system.
There are many excellent systems available. From a business perspective, the ability to work with an existing CMS is more valuable than building your own.
The advantage of using existing code (whether it is a CMS, cart, blog, registration system, CRM solution) is that you can offer people a lot more code, that has been tested, and usually has documentation for both users and developers.
If I were you, I'd look at Drupal, joomla, eZ Publish, MODx, TYPO3, b2evolution, WordPress (listed in no particular order). You can test them out at
opensoucecms.com. These are extremely marketable skills.
You can use NetBeans with any PHP project.