We have this set up. My tile pro built it like a real steam shower, but we didn't install a steam generator: sloped ceiling, glass to the ceiling, transom above door, tiled ceiling, etc. He is an excellent tile professional who has built many real steam showers, so building our "steam-capture" shower was not a challenge for him.

You need to talk to your tile pro about what waterproofing/vaporproofing detailing he recommends. It's been 2 years, so I can't remember every detail of what materials and methods he used, except that I know he used Laticrete hydroban boards and it's a sealed system, not a water-in-water-out system.

You do need to tile the ceiling. My pro used extendable support poles to hold the ceiling tiles in place, and only did one row of ceiling tiles at a time (they are 12" x 24") so as not to disturb the adjacent row. The ceiling took 4 days to complete because of only doing 1 row at a time.

About the door: We asked the glass installer to omit the hinge stops so that the door can swing in and out. After a shower, we leave the transom open and the door pushed inward while the exhaust fan is running and we are getting ready for work. I don't like the door sticking out into the bathroom while we are getting ready. This also allows for easy reach-in to turn the water on with out getting wet.

About the transom: We like having it because sometimes we don't want very much steam to build up. If it's cold out, I close the whole thing up for steam; but if it's hot and I'm sweaty from gardening, I don't want much steam. If that's the case I leave the transom open and I run the fan while in there. Having the transom gives you options. The transom is also useful because you can close the door, but leave the transom open pretty much all the time. This allows airflow which helps cut down on moisture inside the shower. A normal shower has constant airflow because the top is open; it's good for your shower to allow airflow and the transom is the easiest way to do that unless you want the door to be open all the time; I woudn't like that.

Bench: We didn't want a built-in bench. We bought a teak corner bench from Frontgate.

Configuration: Try to position your valve so that you can reach in and turn the water on without having to step into the shower.

Height and slope of shower ceiling: Our bathroom has 10' ceilings. That's too high IMO to get a good build-up of steam; it would all go to the top! So the contractor brought the ceiling down so that the highest point is 8'8" and the lowest point is 8' (this is a 2" slope per linear feet; our shower is 4' deep). This required some framing/bracing work in the attic to provide support for the ceiling tile and the glass above pony wall, so that there would be no support posts needed in the bathroom proper. All the support comes from above. The shower is on the furthest wall from the entry door and a focal point of the bathroom. The high point of the ceiling is against the back wall, so furthest from the entry, and it slopes forward towards the entry. This way, the slope is not even noticable until you are in the shower. Unfortunately, my DS built a steam shower and her contractor sloped the ceiling form right to left. IMO it looks stange/lopsided when you enter the bathroom when it is oriented like that.

Fixtures: We have a fixed showerhead on one wall, a rain shower in the ceiling, and a hand-held positioned low on the wall next to the teak bench. Hand-shower makes cleaning easier. DH likes a cold blast from the rain shower, but not me. He doesn't turn the diverter until the end of his shower, so that he can get a cold blast. I always turn the diverter half way so that the fixed and rain warm up at the same time; no cold blast. It's a luxury, but having that option is nice. Our city allows 2 valves, so our hand-shower is on it's own valve. If you are in CA or another place with stricter water rules, you can put a different kind of value and diverter so that all 3 fixtures are being fed by the same valve.

Glass cleaning: I wipe the shower down a couple times a week, but I don't do it every time like some GWers do. But since the glass goes so high up I can't reach the top. I keep a squeegee in a nearby cabinet, and use it sometimes, but have to admit that I don't do it every shower. Make sure you get the factory-applied glass coating (such as Showerguard).

Privacy: We have a tall-ish pony wall bc I don't like the "shower-show." We've got lots of kids and they sometimes will walk in to ask me a question (yikes!), so I asked contractor to build the pony wall to about shoulder height. What I didn't realize at the time is that I probably didn't have to do that at all because the steam provides a lot of privacy. The glass fogs up and you can't see in or out very well at all. It's also really quiet in there which is cool; feels like you are very far away for just little while. It's very refreshing.

Good luck!