Here's a shot of the Asset Advisors site in process, I typically use a 24 column grid for most of the sites that we build. Although we don't always adhere to those exact pixel dimensions in development.
A little protip: Always name your layers
This will keep you and whoever may be working behind you sane. And ultimately making for a better & happier workflow.
As a freebie, there's a psd attached with the grid, enjoy!