Hi!
Well the best way would to use the point dish screen on your receiver.
Menu 6-1-1
Put in your zip and it will give you the azimuth and elevation for your dish.
When you go up on the roof, you want to have a compass to get the dish in the general direction, also set the elevation acording to your number.
Once you get that, turn the dish slightly left and right until you get a lock tone on the receiver. (You probably want a friend to help you read the tv, and some walkie talkies or cordless phone)
Once you get that signal, you can turn it again slightly left or right to get the highest possible number on the screen. Once set tighten the dish.
Next loosen the elevation nuts and move the dish slightly up or down to where the signal is even higher.
Tighten and you're all set.