So I'm building a responsive layout and I'm reading that I should start with a fluid layout. Ok. But where do I start? Should I build one from scratch and use % and ems and zero pixels width values?

The demo on http://www.initializr.com/ sounds bullet proof. I'd like to use it, but the demo http://www.initializr.com/try doesn't match my design.

Do I start with that demo and edit as needed? What approach do you take?