Content Management, Build or Purchase?

In the past I've created very simple form based content management systems for my clients' websites. I know there are many options available on the market from phpNuke to DotNetNuke and many other open source varieties, however I'm really wary of committing my clients to any of these. However, I need to begin offering better tools to my clients.

Is is better to build your own CMS to better understand the code that makes up the application or is better to invest the time or money in something that has been prebuilt. Any advice, related experiences, solutions?

I'll add that I'm a ColdFusion and WebDNA developer who has recently switched to PHP, so I have a bit of catching up to do as well.

Many thanks to anyone who can contribute to this conversation.

IMO, you should first try most popular CMS' to see what good CMS must have. You said that you just switched to PHP. My advice is too read some book about PHP and SQL before trying to make CMS.

BTW, it's not worth buying commercial CMS' when you have excellent open-source ones, like Joomla (IMO, the best CMS).

wordpress is great for small business / personal sites. Anything larger than that look into a custom CMS or joomla.