BATHROOM SPACE IDEAS - MAKE IT or FAKE IT:

Make It:

If you are looking to add a new bath or expand an existing bath, you can always steal space from other parts of the house -

Closets:  Commandeer a nearby closet (or one already in the room) to enlarge an existing bath.  A large closet can be converted into a small powder room.

Bedrooms:  Who needs that spare bedroom more - an occasional guest or your busy family?  Use the whole bedroom for a spacious bath, or borrow part of it to expand a nearby bath.  A large bedroom can be split into a bath and a smaller bedroom.

Stairs:  Is there wasted space under your staircase?  Put it to work as a small powder room or turn it into storage and convert another closet elsewhere in the house.

Bump-outs: If there's nowhere to go but out, a bump-out or cantilevered wall projection can provide extra square feet for a tub or shower without the need for a full addition.

Fake It:

Stuck with a small space no matter what you do?  You can always make it look roomier.  Try the following perception altering tricks -

Windows:  Replace small windows with larger ones & eliminate heavy window treatments (glass block or window films can be used if necessary, for privacy).  Install a skylight to add  a spacious feeling.

Light:  Chase away room-shrinking shadows with a good source of overall light.  Add supplemental lighting above each vanity sink, tub, shower, and cosmetics table.

Mirrors:  Reflective surfaces double the light and create the illusion of more space.  Beware, however, of enclosing the room in a sea of mirrors, which can be disorienting.