I am creating small bathroom on first floor landing. I'm planning to maximise space by building new bathroom wall jutting out by 600cm at 90 degrees at 600cm level measured from floor of landing level, so that a large alcove exists within the new bathroom. Then I'll insert a basin into the alcove which will be positioned dirrectly above stairs, at 830cm to top of basin, with offset drain. Seems adequate headroom for person on stairs. Can anyone foresee any problems?