Since the OP's post still has no reply...I'll throw out some generic info.
Many rooftop dish installers will not rely on factory wires - adding new cables. If doing a DIY rooftop dish install job, then SAT prep systems are handy to have.
BUT - Rooftop dish antenna's are often blocked by trees and power-lines - a real down side for this set-up.
A switch box is not needed for SAT, if the SAT is wired to feed a separate input on the back of the TV (separate inputs for the DVD, VCR, Batwing, etc.)
The simplest install is to get a portable dish antenna and a receiver...The dish can go on the roof if there is a clear view of the southern sky, or can be placed on the end of a wire where the sky view is clear.
Connect the receiver to the TV input (add permanent coax wires and connectors if needed or desired), connect the dish to the receiver, run through set-up and watch TV. That's just how simple it can be...
That's why I have a Dish pay-as-you-go account, a ViP-211k receiver, and Tailgater portable dish.
DISHForMyRV - Pay-As-You-Go TV: Satellite Service Without a Contract
I also have a single LNB rooftop crank-up dish, but don't even use it anymore, because the auto-aim in the portable antenna is just so simple and will switch between the 3 Dish SAT's without any user action.
Hope that helps