Building a portal from scratch or acquiring a portal engine

Does anyone have a pro's & con's list or can provide some insight on the effort it would take to build one from scratch?

Your question seems to be little confusing. Do you want to develop a Portal like the ones provided by Apache/Liferay/Jboss or you want to develop a Portal based website. If you can clarify more probably I can help.

Sorry for the confusion. I think what I am trying to ask is: Is it possible to create a portal based website using portlets w/out using a portal server like Apache/LifeRay/JBoss? If so, is the effort "large" or would you just recommend using a portal server?

To develop a Portal or to convert your existing application to Portal you need to have a Portlet Container just like some servlet container.

Now as I told you there are some open source Portal Servers available in the market from Apache, Liferay and so on..

Thing is if we take Liferay for instance then it not only provides you a good framework to develop your Portlets but also provides a number of Portlets like Blogs, Message Board and so on which can be used as it is or can be customized. Also with some customization you can change the look and feel and get your website up and running.

Liferay is free so if you decide to use it liferay.com will be the best place to start.

If you need any help in deciding the platform or for getting more inputs on this just let me know.