Talk to your builder ask for vinyl flooring glued around perimeter [takes 20 seconds to remove] and 1/8" thin shower enclosure glued to drywall. LOL

You need to first determine whether the builder can accommodate your request and at what price. If they can do it, I suggest it will be a lot more convenient than going into master bathroom remodeling mode after move in, trying to finding a competent tile setter willing to do a small scope job working directly for a homeowner, and you'll only need to deal with a single entity if there are any warranty issues.

Vinyl floors and something like Vikrell or Sterling tub or shower surround panels.

I just installed click together LVP on two bathroom floors. In theory, you can easily unclick it and use it somewhere else.

Will your house appraise for the loan with house trailer finishes everywhere? Will your builder even allow you to downgrade it like that? If you’re buying it at closing, the answer will be, nope, not a chance. If you own the land and hired the builder, all it takes is more money at closng, and then a complete out of pocket cash 60K+ remodel of the bathroom, after closing. If youre thinking that will be ”cheaper” than getting what you want right now, you havent priced remodeling, or waited 18 months for the right contractor to actually be available for the project.

I don't think the question is whether there is a minimum level of flooring to pass inspection as you could theoretically have just dry wall in a bathroom and cheap vinyl tile - the caveat being that the shower needs to pass inspection so it has to be properly constructed - at least in my location.

Like others have posted, I don't understand what you would gain by not selecting the finishes you want and having them installed by the builder. This would be especially true in a bathroom where there is presumably a shower of some kind which requires waterproofing of some kind and has to remain intact in order to preserve its integrity as a waterproofing system. Also there are "finishes" in a bathroom (and elsewhere) that also are generally categorized as low end builder grade - e.g. counters, faucets, sinks, shower fixtures and even toilets - why the focus on the tiles specifically? As others have posted, finding skilled tile workers to properly build a shower and even just install is hard and presumably your builder is skilled and hires skilled tradespeople so you would be better off using his expertise and labor base and then also being able to deal with any issues direclty with him rather than chasing a tile setter/tradesperson you located on your own.

It's hard to say what impact this will have on the appraisal. I consulted (about other things) on a job with a luxurious master bath with one of those showers that required a special pressure system, a separate water heater and so forth. To save money, the two other full bathrooms had those shower or bath surrounds that were acrylic, could be attached just to the studs, and vinyl floors. All plain white and inoffensive but inexpensive. And this was not an inexpensive or small house, overall. The house was sold again soon after and the owner bought a smaller house in the neighborhood. The inexpensive secondary bathrooms were not a negative in the sale apparently. And guess which bathroom suffered a major failure after about 8 years, requiring a full gut renovation? The full-tile, fancy master bath.

It does seem that you may be wasting some money if you install functional but inexpensive baths only to remove them immediately. But I am not sure how much the appraisal is going to be affected by bath finishes. At the other end of the spectrum, for example, I don't think a house is going to appraise a lot higher if it has a $7000 Kohler Eir toilet than if it has a $500 toilet. The problem may be that this is for the owner's bath rather than secondary baths.

See what the applicable permit requires. Do that by talking to the building department inspector. Let him know what you want to do and ask for his suggestions. Bathroom floors aren't waterproof except in a wet room design. Japanese baths have them often. For the shower he's likely planning on waterproof prep for the tile he intends to use. Probably all you need with the fixtures installed. Schluter products are a good place to start. Link.

And it's vaporproof in case you want to make it a steam shower.

The biggest question is how much of a credit the builder will give you for installing less material or less expensive materials. I know someone who wanted to buy two adjoining units in a condo and asked the builder what the credit would be for leaving out an entire kitchen. The credit the builder offered was Negligible, like a few thousand dollars, and that was for leaving an entire room empty of its normal contents.