In my area the builders won't even consider a purchase based on the sale of the buyers current home.

Does the contract you are considering with the builder contain a contingency clause for the sale of your home? Are you considering selling your current home with a Realtor or FSBO? This could also affect your builders perception of your ability to sell your home timely without causing any delay in the new home purchase process.

If you need the funds from the sale of your current home, strongly consider selling first before you buy the next home.

Edit: It makes sense that the builder would want to see at least a CMA (or an appraisal) to see if you are realistic in your planned sales price if your purchase is contingent on selling your current home. It is very common for sellers to overestimate their home's value especially when buying a new home. No builder wants to have the buyer cancel the purchase months down the road because the buyer couldn't sell their current home or the proceeds were not enough to allow the buyer to qualify for the purchase even after the sale.

If you can’t pay cash, then they need to know how you plan to fulfill your sales contract. Contingencies mess up everything for everyone. Better sell fast, rather than trying hold on to to sell high. You don’t have the luxury of time when you are dependent on that domino falling first to trigger all the rest downstream.

If you can’t fulfill your contact, they will then declare the contract void, keep your deposit, and then sell to someone else. These were all things to think about before you agreed to buy a new build.

Buying a home contigent on selling a home is essentially a contract saying “I might buy your home, if all the stars line up.” Contingencies are an OUT to a contract, and home sell contingencies are the worst kind because the seller has little control over the domino effect the buyer has placed them in, yet the seller will be the one who bears the burden of the deal falling apart. This is magnified with a new home build because builders always have sunk costs even before the first shovel hits the ground, permit fees, soil tests, engineering fees, staff time, etc. Thousands are at risk, I am surprised a CMA is all that was requested. Additional requests to play the contingency game could be non-refundable deposit (skin in the game on your part), approval for your marketing plan, list price, and price changes as needed to get the home sold, etc.

Never met a home seller that didn’t proclaim for certain their home would sell right away at the price they want, yet the number of listings that don’t sell and expire is pretty high.

As for the argument that the builder can just sell the new home if you can’t perform, it will likely be at best sold for cost, or even a loss. If you could buy a $500,000 new home where someone else got to pick everything, or a $500,000 home where you get to pick everything, which one would you choose? Your builder sounds naive if all they are asking for is a CMA.

Is your new purchase contingent in any way on the sale of the home? If so, it's not unreasonable, I suppose. If not, tell them to pound sand. None of their business.

The request for a CMA is almost certainly due to a home sale contingency. You shouldn't "suppose it's reasonable", but assume it's a standard inquiry that a seller would ask for some background on the home (the CMA) that the buyer is using as a contingent "OUT" for the contract with the seller. How else is the seller to make a judgement on whether you can perform? This would be standard in re-sale as well, not just a new build. Where you plan to get the funds to purchase a house will need verification, whether it's all cash purchases, financed through a bank, or funds coming from sale of a home.

But go ahead, tell them to pound sand, and while your at it tell your lender to pound sand also when they start asking to verify whether you can perform, and see how far you get with your new home dream.

Personal Information is provided by me only on a substantiated "need to know" basis. "Want to know" is insufficient. The Buyer has not provided sufficient information to answer this question, unless I have missed something.

Yes, any time personal information is demanded and is not required by law or by contract to which I have provided informed consent, there will be resistance. You are free to choose otherwise, of course.

Perhaps the Buyer has other cash assets on which he is relying. We just don't know and cannot proceed with reasonable answers until we do.