Not as complicated as you are thinking. Assuming you are planning on putting the bathroom directly above your current bathroom you can tie the waste line into your stack(should be exiting out of your roof) and pulling supply lines up is not a big job. I did exactly this in my three story row.
Dude_Love4 t1_jdfkom9 wrote
Reply to Rowhouse bathroom addition contractor recommendations? by andrewbt
Not as complicated as you are thinking. Assuming you are planning on putting the bathroom directly above your current bathroom you can tie the waste line into your stack(should be exiting out of your roof) and pulling supply lines up is not a big job. I did exactly this in my three story row.