A deist cannot get "outside" of creation long enough to know anything about God. C. Van Til sees a separation between the creator and creation and argues that no one in creation can vault his way up to the creator -- the creator must reveal himself to his creation.
A deist is likely going to have to work from either the Cosmological Argument for the existence of a God (notice, I still don't think he could say anything about what that God is); David Hume among others refuted that well. Or the deist may work from the Teleological Argument, which in part depends on natural revelation: that the world shows evidence of intelligence and purpose -- however, once again, one would find it logically impossible to therefore demonstrate that a God stands behind this intelligence and purpose.
There are lots of sources for this kind of discussion. Mr. Van Til, as I already mentioned, and Louis Berkhof's Systematic Theology discusses these points in his section on The Doctrine of God.