I gotta weigh in on this one, as I am an attorney.
You have a contract which specifies a particular method of performance, i.e., you are entitled to receive a 9 foot pour in your basement.
The builder is in breach. However, this does not normally entitle you to avoid the contract entirely. To avoid the contract would require that the breach be material, which is legalspeak for "basically in violation of the fundamental essence of the contract, rendering proper performance impossible." Like if he built a 2 story house instead of a one story house. Something very major. Whether this is such a breach or not is up to a court to decide as a matter of law. But, if YOU materially breach and then the court determines that the other party's breach was NOT material, then YOU are the one in the hotseat. You are NOT entitled to breach a contract merely because the other party has himself breached it.
However, as the victim of breach, you are entitled to compensation for the difference in value between what you contracted for and what was delivered. Whoever says that this is hard to figure is full of sh!t. You get appraisers in there, expert witnesses, and they do an evaluation of how much more a house would be worth with one configuration versus another. Courts do this crap all the time. You think this is the first suit ever over a custom home? Happens all the time and courts routinely fix damages.
Your first step needs to be to figure out what your damages are. Certainly "lack of enjoyment" is worth something but don't expect to win a "huge cash award" like they advertise on TV. You haven't lost the enjoyment of your penis or arm or your child or anything serious. It's one less foot in a ceiling. You won't likely get squat for that. Essentially, your damages are roughly whatever the house is worth as delivered versus as contracted.
When the builder tells you that you can escape the contract and he can sell it for more tomorrow, tell him, and I quote, that he can shove that idea up his ass. If he is so confident of this, counter with the proposal that he sell it tomorrow and give YOU the excess proceeds and then you will walk away. I'm sure that'll go over smashingly with him.
Your tack of argument MUST remain: I don't give a sh!t what you can sell this house for tomorrow or if you can con your own damned mom into giving you her left nut for it, you are obligated to deliver this house AS CONTRACTED and that is what you are going to do. If you cannot do that, then we must discuss remuneration to me for your FAILURE to deliver this house AS CONTRACTED.
They are NOT doing you a favor by rerouting the HVAC and all this other bullsh!t in order to placate you. Find out how much the 8 foot pour diminishes the value of the home. Take the HVAC reroute, free windows, and plumbing joints PLUS the difference in value.
THEY are the ones in the wrong here. You are not. As such, you have to examine this from their perspective. How much will it cost them to conduct a court fight with you in which you stand a high likelihood of recouping your attorney's fees plus damages? THAT is what YOU should charge THEM for not suing their stupid asses.
The only thing THEY have going for them is that YOU really, really, really, really want this house and are willing to overlook their failure to perform in order to get a house. Car salesmen use this ALL the time to SCAM customers. So, they throw in some wood shift knobs to get buyers to buy a car they are not really happy with. This is bait and switch. Demand what YOU contracted for, what THEY offered, what you severally agreed upon and what YOU are paying for.
I mean, I see this from the plaintiff's perspective. You are going to let them get away with giving you a house of substantially less worth plus the cash necessary to bring it up to par with a 9-foot poured house. AND, they are going to additionally add value to it instead of spending the same cash value on their and your attorneys to fight a case they are going to lose. They KNOW that the $3000 windows are worth $1000 in parts and $500 of illegal day labor, whereas the attorneys REALLY cost $3000. IOW, it is in THEIR best interests to give YOU $x in value in the house instead of actually spending $x in cash because they can add that $x in value for way less cost than $x.
Also, they've got hotel bills to consider for all this extra time it's gonna take to complete, appraisers' fees, architects, experts, etc., all the costs you're going to pray for in your complaint.
First step, get a professional to assess the difference in value.