The pipe going to the roof is the vent...you will need to move that. It is connected to (at least) the shower drain, so when you move the drain, you'd need to break that as well. You could cut it off in the attic, run it up a convenient wall, and reconnect the new stuff to that pipe going through the roof, or replace it all the way through the roof. Since the vent doesn't normally carry water, replacing with pvc is probably the easiest thing to use. Below the floor, the toilet probably also runs to the pipe that goes down to the basement. Depending on the orientation, that may be the vent for both the toilet and the shower. Not sure if that is correct. In the attic, do you see anotherpipe coming up from behind the toilet, and connecting to that pipe thatgoes up and is exposed? One of the pros will have some comments...