Second Floor Washroom Rough-in

I've searched around a few sites looking for an answer with no luck.

I plan on adding a second floor to my home which will include a full washroom.

Right now I am renovating my main floor washroom and I am wondering what I can do now to rough in the toilet and shower drains.

My thought is that it would be much easier and cost effective to incorporate the 2nd floor washroom above the first floor washroom (which is above the basement washroom). If I need access to the main floor washroom I'd rather do it now than rip everything up in a year or so.

Cheers

Tie into the 3" drain line outside of the 1st floor bathroom and put a 3" drain stack in a 2" x 6" wall. Run it up through the wall and above the ceiling height of the 1st floor bathroom. That way, all you have to demo is the ceiling of the first floor to run to the toilet, lavatory, and shower.