What’s below the room? Is it basement? Is it accessible?
The biggest issue with adding a bathroom to a space that doesn’t have one deals with the waste plumbing. The toilet requires a 3” waste line and the sink requires 1 1/2” pipe. The toilet is where you run into issues. Getting that 3” line to run somewhere without removing structure can be difficult. Hopefully you get lucky, but that’s the big issue. I have never met a plumber that would do a proper job of running a 3” line through structure. They all hack it apart and compromise the home. I’m in the middle of 2 bathroom rehabs that had this exact problem.
If you’re lucky, the waste runs will be easy and accessible. If you have basement below and you are ok with pipe below the floor joists, that makes it easy too.
Beyond the waste line, you need to make sure the bathroom is vented properly, which may require installation of vent pipe above your bathroom. Then you have supply lines for the sink and toilet. Those shouldn’t be an issue as they are typically 1/2”.
Figure on a plumber being pretty expensive for this. 4 figures plus wouldn’t not be unheard of.
Sent from my iPhone using Tapatalk