I've been thinking about this and collecting parts for at least a couple of years. Thanks to everyone on CNCzone and elsewhere that has posted pictures and info of their CNC machine builds. Especially: 5bears, Bob Warfield, Guldberg, JH-Q, S_J_H, The Blight. (edit: how could i forget mackeym !)
I started with a 18x24x3 Granite surface plate. I drilled half way through from the top and then half from the bottom. All the components will be bolted down rather than using epoxied inserts.