Hi John...
I have a few thoughts here, OK?
First, I wanted to pop in and tell you that building a floor up will actually take about the same time it will take you to install plumbing pipes underground. Here, purchasing/picking up and installing the lumber and the plywood and building the step up into the bathroom takes about the same amount of time it does to rent a chipping hammer, dig out the floor, install plumbing and backfill and recement. I know it is hard to believe in some ways, but it is true. Don't forget about the funny step at the doorway or the headroom issues and just how the whole bathroom can seem offkilt.
I can point you to an entire thread by a poster named mechanickid that started out as your thread is starting and he finally gave in and did it correctly and boy oh boy was he glad when he was done. Click on this link to see that thread...
please read the entire thread to see how it ends and how we finally arrived atthe conclusion we did. He even posted pictures as he went along...including the end result!!
https://www.askmehelpdesk.com/plumbi...om-252241.html
Review the thread by mechanickid and then pop back with your thoughts, OK?
Finally, have you looked at the SANIFLO systems where you install a macerator pump...no need to build the floor up exacept under the shower...;) Click on this link for more info.:
Installation of pumps, grinders, and toilets for the home | SFA
Back to you...
Mark