The question in your case is whether to use a ready made CMS or to create your own system using a framework. The right answer depends on the following:
- budget
- number of users you will have (long term performance concerns)
- further maintenance
- total number of details (bells and whistles) you want to provide on the site
- implementation with third party/custom APIs
- special/custom features that require high level of freedom (example: StackOverflow reward points and badgets)
As this is a question most of us face pretty often, here are cons and pros of a ready made CMS vs a framework:
Ready made CMS
Pros
- faster start and development time if your project generally fits in what the CMS provides
- available modules and themes
- backed up by community, meaning that new features, bugfixes, support, tutorials etc. will be provided to you free of charge
- unified set of standards - it's easier to continue working on an existing CMS site than to take someone else's custom application (this is relative, but the point is that in a site that uses an existing CMS most of the things/setup will be familiar to you while in a custom app the previous developer had more freedom)
- security is something you do not need to worry that much as in a custom app
Cons
- if your requirements are very specific, you will need to override the default workflow of the system; in some cases this can be tricky and will make you spend more time than to write your own
- redundant code in modules/plugins
- performance - a ready made CMS will rarely be as fast as a custom made application
- not suitable for every large website (unless you fit in almost everything that the CMS provides)
- steep learning curve in some cases (Typo3, Drupal)
Custom application
Pros
- it's up to you to define the structure and the logic of the application
- app design is made especially for the project you are working on - so there is no redundant code
- freedom to do anything you want
Cons
- expensive - in most cases you/your client will need much more money for a custom app
- further maintenance will be harder
- changes and modifications of the structure can be very time consuming
- if you aren't using a CMF you will have to reinvent the wheel in some aspects
Bottom line
Spend a couple of days and learn something about the CMSs out there, such as:
- Drupal - my first recommendation; good for medium to big websites; good community; medium/steep learning curve
- WordPress - my second recommendation; good for small to medium sites
- Typo3 - enterprise level system; pretty complex, combined with a framework which can be used standalone in projects
- Joomla - I personally don't like it and do not recommend it because of amateur plugins, but it is popular
- SilverStripe
- MODX
- Concrete5
I think that any bigger and serious project, which will have at least 1-2 programmers to take care of the system at all times, should be custom. Exceptions are only if it fits exactly in what an existing CMS offers already.
Hope this helps :)