I got the glass through a local shop. My situation was different, as only one wall, the "front" door wall, was glass. The other three walls were kerdi and tile. The sloped glass ceiling was captured in the walls on three sides and clear silicon was used to seal the remaining side to the front wall of glass. I'm not sure what type of specific seal was used on the door. It might have been clear vinyl. If you do a search or ask at the glass shops, it might also help if you refer to it as a "raked" (sloped) front wall of glass. Actually, lemme see if I can get a quick google hit... Found one at Wilson Glass. Not exactly what you're looking for though. Using something like that with a sealed transom overhead would work and be the lest expensive. Having the front wall as a single piece of glass with the door cutout of it would be $$$$$.

We put one into our basement bathroom remodel. Because we did a total gut remodel of the entire house we were down to bare wall studs. We opted for a tiled steam/shower, custom done to the room's specifications, with a sealed glass door. We used a steam generator unit that was installed in the garage (you can install it up to 20 feet away from the shower itself). The inside of the shower has a built in bench, thermostat, shower, and light. Our tile guy went to great lengths to make sure the ceiling was sloped the proper degree, and the tile was placed in it in a very balanced pattern. Now we're just waiting for the electrician to return and finish connecting the light and the power! We redid 2 other bathrooms upstairs, so this was more a guest bath on the way to the hot tub off the basement laundry room. It wasn't that expensive to do, and we had to finish the bathroom anyways. Adding a steam generator and making the necessary changes to the tiled shower wasn't cost-prohibitive.

Stick with the steam that is the most confort as far as its not dry heat like a forced hot air. Why anyone would go to forced out air is just taking the cheap way out. A hot coil in an air handler will work better. Also have e you thought of radiant floor system at all or off the return of your boiler you can have a circulaing pump and add baseboard to the new room. if 75 gallon water heater isn't cutting it you may want to try a tankless water heater. Don't go with forced hot air you wont be happy. Here would be my options that you can run by a good plumber. 1 tankless water heater to do radiant floor or coil on a air handler, with a heat exchanger you can also do domestic water and never worry about hot water. the neg side about this is tankles has to be on a maintnace program for scalling and general PM. 2 put a B&G pump on the return of your steamn boiler and use that hot water to do a basboard or new radiaters in your new addition. for your a/c I would go witgh a ductless systeem if its only one big room. here are the three manufactures I would go with 1. tankless I would go with takagi ( make sure its sized correctly) 2. air handler I would go with first company. 3. fujutsi if you where using a ductless. If it was my house I would use high baseboard and heat it only to 140 degrees stick that on a tankless water heater and get my domestic hot water thrue that also. or radiant floor instead of baseboard. Use the fujitsu unit for the a/c of the house.

It's seems super hard to get comparison info. Also debating between Thermasol and Mr Steam. We were leaning toward Thermasol, but just has a plumber over to give us a quote and he had never heard of Thermasol and has done lots of Mr Steams installs. There seems to be 3 key factors that I'm considering. The constant steam of Thermasol seams to be a big draw. Although the automatic auroma of the MS seems lots better then manually doing it. The Serenity Light, Sound, Rainhead looks amazing, but it cost $2k and then you also need a $1,500 digital shower valve. I'm a little worried about all the gee-wiz stuff on the Thermasol that may wear out sooner in the long game.