Is it OK to install a second roof deck on top of the original roof deck? Could a vented nail base be used?

Here is some information about creating a 2nd roof deck and using vented nail base.

Some situations require the addition of a second roof deck on top of the original. These cases require some special steps to ensure that the system will perform properly. A vented nail base could be used in these cases, however make sure the air space is sufficient. The best way to apply a second deck is to lay 2 x 4s down on edge similar to a rafter and apply the new deck over 2 x 4s. This will yield an airspace of roughly 3 inches in height which should be more than adequate. Be sure that the intake vent detail accounts for a path for the air to go from intake vent opening to the new vent space. Another important aspect to consider is condensation control. Moisture must be a given an easy path to pass through the airspace. Thus, provide holes in the original roof deck so any moisture that does get into the insulation under the original roof deck can work its way into the new airspace and be vented out. If the holes are not cut, the original roof deck will be at outside temperatures because of the new air space directly above it and the trapped moisture underneath it will be able to condense on the underside of the original deck.