What is the smallest building reg size shower room you can build?
Basically Joan you need to have enough room to make all facilities functional, i.e. you must have room to use them. If you think of a small en-suite with a shower, sink and toilet then that should give you some idea. Play around with the positioning of each facility and that may help you. Remember that to get planning permission local councils don’t look at what you want, they look at what prospective new owners need. A 800mm shower is ok, i know i have 2 in 2 en-suites. Good luck.