A bathroom in a Banbury stone building raises a question that a bathroom in a brick house does not: what a sealed, wet room does to a wall that needs to breathe.
Solid stone construction handles moisture by letting it move through and evaporate. A bathroom is the wettest room in a house, and lining a solid stone external wall with an impermeable tanking membrane and porcelain traps moisture inside the wall with nowhere to go. On an internal wall that is fine. On a solid external wall it needs thinking about, and the answer is usually a breathable build up on the external wall with full tanking confined to the wet area itself.
Routing waste is the second constraint. Cutting a large penetration through a thick stone wall is not something to do casually or repeatedly, so a bathroom layout here should be planned around a minimum number of penetrations rather than moved freely.
Floors bring the usual older building considerations: joists sized for a bedroom, not for a filled bath on a tiled floor, and permitted zones for any notching or drilling. We will move a fitting a foot rather than cut a joist where it must not be cut.
Ventilation matters more in a solid walled building than a modern one, because the fabric is less tolerant of trapped moisture. Our bathroom installations page sets out what a full refit involves.