I can't speak for the KBRS, but the TileReady and the Schluter foam tray? TileReady: You set the base, it is water and vapor impermeable by itself, so the base itself does not need any CPE or CPVC liner or membrane on top of it. You'll want to seal the wall vapor barrier to the top flange of the pan. That way for a steam shower you'll have an integral vapor barrier on the ceiling and walls, and by sealing the wall barrier to the pan, the shower floor will become integral too. You tile directly on the surface of the TileReady pan. Schluter: The foam tray gets set to the floor. You'll then need a water/vapor barrier on top of the foam tray, but not CPE or CPVC. You use Kerdi membrane. Kerdi the ceiling, the walls, and the sloped tray, and you have an integral water and vapor proof barrier throughout your shower. All you have to do is overlap the membrane by 2" and the seam is good to go. Waterproof and vapor-tight. You then tile right on the Kerdi membrane. Kerdi is the only thing I'll use for steam showers, and it's pretty much all I've used for regular showers for well over a decade. Regardless of what system you use, any you mentioned or any other type, you want the floor membrane to be sloped. You do NOT want the membrane flat on the floor, then sloped mud and them tile over that. The membrane itself has to be sloped. In the case if the TileReady, the surface of the pan is the membrane, and it's sloped. You're good to go with that. With Kerdi, if you put it on the Kerdi foam tray, the tray is sloped, so the Kerdi membrane will be sloped. You;re good there. If you use a deck mud slope under the kerdi, and thinset the Kerdi to the sloped mud, again, the Kerdi will be sloped since it's on a deck mud slope, so you're good to go.

Pete summarized the main points nicely, though I'd disagree that solid surface pans are all ugly. Plain, perhaps, but I don't think they necessarily detract from the look of a beautifully tiled shower. But in the end, aesthetics are a personal opinion, so only you can decide if it matters to you. One more thing no one mentioned: pre-fabs are idiot-proof. If tiled floors (and all the stuff that goes underneath) are not installed correctly, you can end up with a mess on your hands. But you don't often see GW horror stories entitled "my contractor screwed up my solid base shower!" :-) My sister has a tiled shower floor and complains of discolored grout. That's what drove me initially to do a solid surface pan. Ease of install and idiot-proofness were bonuses for this DIY-er. And I like it fine. We're done with all the bathrooms in our house, but now that I'm much more informed about shower construction, I'm likely to try a fully tiled (and kerdi'd) shower in a future bathroom project, should it materialize someday.

i am wondering why so few are using Terrazzo now. https://www.houzz.com/photos/cedar-park-residence-13-contemporary-bathroom-seattle-phvw-vp~92378-Park-Residence-13-modern-bathroom-seattle https://www.houzz.com/photos/berkeley-kitchen-and-bathroom-contemporary-bathroom-san-francisco-phvw-vp~3505073-Kitchen---Bathroom-contemporary-bathroom-san-francisco

phoenix, As you know, there are upsides and downsides to each. You buy a prefab unit and "you get what you get". You get a certain size, with certain features, made with certain materials, created in a certain design style. The size, features, materials and style may be everything you want. Perfect. In that case, you can have a unit up and running in minimal time. With a custom steamer, the choices are yours. You'll need to self educate or work with a capable builder/installer so the design is correct. That construction is correct. That you have a vapor barrier (not just waterproofing, as "waterproof" does not always mean "vaporproof") within the assembly. That you'll want to select material finishes based on aesthetics and performance. That any lighting, venting, etc, needs to be appropriate for a steamer. That the steam generator needs to be properly sized for the volume of the unit and the surface materials used in the unit. The location of the steam head needs to be considered versus the location of the user. It goes on and on. I don't have a recommendation or advice for free-standing or prefab units. Not that I have anything against them, I just don't have enough familiarity with them to offer a recommendation. Vetted peer reviews from existing owners would probably be your better bet. For site-built, the basics? I recommend cement board as the tile backer board. A vapor impermeable topical sheet membrane to go over the cement board. Porcelain tile (no natural stone, most will absorb and hold moisture) as the wall covering. While others are adequate, I recommend Thermasol steam generators. Other materials will work. Those are my general guidelines. With a prefab unit, if anything goes wrong, you may simply have one-stop shopping for problems with the unit, especially if the unit is installed by a company rep. You simply call the manufacturer. That can be very convenient. With a site built steamer, you may have several trades involved int eh construction. You can have installation issues, material issues, equipment issues, etc. The plumber can point at the electrician who can point at the manufacturer, etc. If you have a GC, then the GC will be your go to guy. If you hire the subs yourself, then you;re the one trying to resolve discrepancies. Best bet is to find a reputable company that has been around for a while, and a reputable installer who's not doing his first installation. Have a thorough conversation beforehand so you understand the particulars of any installation (prefab or custom) before any work begins. Good luck.