Rent the biggest, electric saw (with a diamond blade - for concrete) -
"Wet or Dry" is good.
Probably, it will be 9" to 10" (It depends on what's available in your area).
You can rent gas fired saws (If you like to smell/breathe Carbon Monoxide -
Saw a couple of parallel lines (where you're going to run your waste lines - saw them a little wider then you think you'll need) -
We would saw another line in the middle of the two lines - then: it's
sledge-hammers - electric, jack (rotary) hammers to bust out the concrete
floor (eye protection/dust masks!).
Whether or not the blade is "Wet or Dry" - spray bottle of water can help
to keep the dust down! (Remember: electric saw = a shocking experience!)
Make sure you pitch/slope your drain pipes, to your "plumbing stack"/drain - a slope of 1/4 inch per foot is considered good.
Don't try to saw through the floor, to the total depth that the saw will
allow - use, repeated cuts, deeper and deeper - an 1/8" to a 1/4" to a 1/2" - and so on. (I know - time consuming: but, easier on the saw/blade!).
(Don't try this at home!!)
We've done this dozens/hundreds? of times - didn't count - don't remember.
Hope this helps!
(Glad you're doing it, and not me!!