Yes, you probably have to retile, mainly to make sure you have a cement board backing for the tile in a steam situation. And be sure to slope the ceiling to the back wall, because steam will condense there and want to drip on you. Many older tile installations were just over "greenboard" drywall to save money. Opening up the wall has other advantages: more insulation, access to new supply lines and fittings, and blocking for grab bars to mount securely, or backing for a wall-mounted flip down shower seat. Good luck!

If this was my house, and wanting what you want, maybe see if the builder can not build your shower at all and allow a real pro to come in there. Steam showers are really nice, but really really require a pro to build them. I doubt your builder has said pro on staff. Plan on over 10K to build the steam shower. If your builder or any other GC, tiler, etc. says you can do it for less, they are probably a hack, and you will have a poor outcome with mold and water damage. But a real pro can do it. My DS has a steam shower. It can be done, but you need a real pro, not the builder.

Steam showers require vapor proofing. That’s a skill level well above waterproofing. Builders don’t even do waterproofing well. Get the cheapest plastic surround possible, with a shower curtain. Then have the expert build it after close. Skip the body jets. They don’t get used.

Thanks everyone! My husband and I will definitely talk through all those comments.

The body jets were because I have spinal damage & they’re very helpful for muscle spasms (plus adding jets gets us a second tankless water heater for free).

Here‘s the layout as it stands - we go to redline next week so your comments are appreciated!! I want to switch the shower and tub so I don’t hear my husband showering through the bedroom wall.

Counters will have vessel sinks, and bathtub is 72”, so trying to keep an upscale look without just throwing $$ away - we by no means have disposable income.

Well. Lots of room for improvement here. You are not ready for a "red line". If you mean red line/sign on the dotted line to build the house? Post the plan in ENTIRETY. As what I see in "partial " form is a very long tunnel to the original problem.

Re Bath,

If you are doing a tub " for a high end look" and not frequent use? Eliminate it. I can't tell what you had in walls on the original, you have blue lined it into a total messy wreck. But a 10 x 15 bath can look a lot better than what you just posted in layout.

What's the purpose of double doors?

A glance nearly 24/7 into your closet is high end? Where if any windows in this bath? Over the tub?

A loo jutting into the middle of nowhere?

No............post the ORIGINAL plan, that clearly shows all the dimensions, walls, windows everything.. This plan stinks on all counts : ) inclusive of vessel sinks.

Jan people come here to ask questions, not be berated. If you’re a pro (which is what appears next to your name), maybe the action here is helping you to understand how you approach is abrasive and disrespectful?
Perhaps saying to me “thanks for what you posted, but could you post ‘x’” would be a way to engage me and kindly suggest I should back off the redline meeting - and I don’t know about elsewhere but here in Texas you have to sign to purchase a build weeks or even months before you redline.
I’ve built 4 homes and lived in them, I’m always looking to improve on our homes in a thoughtful way and really appreciate any help but I’m not here to be disrespected when I’m spending hundreds of thousands of dollars on a house. Our house will only be 4,000 sq ft, not 20,000 so I’m sorry our commode area goes into “nowhere”, but that’s the layout we’ve been given. Oh and that view of my closet? Yep, I want it. 24x7. It’s being done by a closet design company and has a big chaise lounge in the middle with lots of shelving and glass doors, and beautiful lighting, so I’ll be looking at nice handbags and jewelry, not manky old clothes...and that makes me happy.
I’ll close by saying I really appreciate the comments of those who posted with the purpose of HELPING me.
I guess I’ll

I'm not berating you. Almost never does someone focused on one aspect of a plan for a single room really see it. Same thing can happen with a room within a house!

You certainly want the most for your dollars in both comfort and function . Please post the original.... ? Apologies for delivery..... but yes it can be better.

Try talking to a steam shower installer now. You'll get some guidance on what has to be done now, what can be replaced later, and what the overall costs will be. Ask specifically about glass enclosures, if that's what you want.

An enclosed shower is a joy forever to mildew and mold. See if the steam shower pro has some advice about ventilation. A very large ceiling fan at the code-required distance may assist in circulating air if you leave the doors open and keep the exhaust fan on a timer after showering for an hour or whatever it takes in your climate.