What does it take to create a social networking cms like phpfox or socialengine .

I am interested in using php / mysql .

However , I want it to be modular , like above examples . Like I can enable disable videos from backend .

Most important , it should have ability to allow others to extend it , like facebook applications .

Should I follow a framework [ cakephp or something ]?

Should I use some pattern [ factory or singleton ] ?

Is there any book available on subject ?