FWIW I went through this decision-making process for our shower room. We (she) wanted a big shower area, and having made a few scale models (complete with 1:50 scale model lady in a bikini in the shower - I kid you not) we (she) settled on a minimum acceptable shower area of 2000mm x 900mm. I made the shower room 2010mm wide, and then had a long, hard think about how to construct the shower area. In the end I chickened out of fitting a wet room former, as I know my tiling is crap, and unlikely to improve (I hate tiling with a passion). I found a local supplier offering a 2000mm x 900mm low profile shower tray (not cheap...) and opted to fit that. I set the tray on a flexible tile adhesive bed (it was one of the very heavy ones, ~70kg) and then fitted 9mm marine ply to the rest of the shower room floor (glued and screwed to death) and had 12mm travertine laid over that.
We're very happy with the result. The tray only projects up about 20mm above the travertine and so there is no feeling of stepping up into the shower. I did have to fit the 50mm drain under the floor though, but as this was on the first floor it was reasonably easy. The Gods were with me, too, as the openings in the Posijoists allowed a straight run to the soil pipe stack.
Probably of more relevance to your case is the shower bath I fitted at our old house. That had a larger, lower, shower area, and the floor beneath was concrete. I didn't find it too much work to Kango a channel across the floor for the waste pipe, and make a hole under the bath trap. After fitting the waste pipe and testing it, I just fitted floor tiles over the top of the channel. That lasted a bit over 10 years with no sign of any problem.
Finally, because I hate tiling, I used AB Building Products Multipanel, both in the bathroom of our old house and in the bathroom and shower room of our new house. I'm dead impressed with this stuff. Far quicker and easier to fit than tiles and no nasty grout to try and keep clean. The only snag with it is that the standard bottom edge seal is complete and utter crap, and should have been binned as an idea years ago. Easy to get around though, just space the lower edge of the panels up by around 4 or 5 mm with tile spacers, then just run sealant into the gap. Let that cure and either run a finishing bead of sealant, or, as I did (I hate cleaning grotty sealant too) fit a PVC trim bedded on clear sealant.