A room about the size of a master bedroom would be nice. If your building a small home a room that size shouldn't make the house layout a bit odd.
Now if it was to be a separate building, a room the size of my husband's shop would be wonderful, 24x 30.
And I found this house layout. It has the perfect size sewing room.
https://i.pinimg.com/originals/e8/96...aae9172805.jpg