I have my own codebase like stolzyboy did. It is clean, simple, expandable, flexible for our team. The best of it is that the art/creative designer can just use traditional html approach to reformat the user front end page as WYSIWYG. And the backend admin is consistent. The site owners (our clients) can catch up in 5 - 15 minutes. And I can add new features/modules/functions etc. easily. I have used 3rd party systems in quit a few projects too such as phpbb, occommerce, zen-cart, drupal etc., and I also keep on using 3rd party as my study and reference tools.
It is 50:50 cases based on php developers own choice, 3rd party or your own codes.
But when I look at the local php developers market. It seems that no employers are looking for php developers with his own codebase, even that codebase might be great (portfolio and quick check on the code can tell that.), most employers are looking for php developers with extensive experience on certain 3rd party systems. And even on the 3rd party systems, the systems require less experience overrule the ones require more experience. (such as drupal developers overrules code igniter developers). Or so many of the employers require MVC etc. (MVC or not, I thought it should be an option.)
I was wondering if I should follow the industry trend (not necessary the developers' trend) later on, maybe I should just do it earlier. So far, 3rd party or my own code base, or which 3rd party, I still use my own call, but how long I could continue to do that?