What to do in this situation? (

You should sue the building and the broker as well, for time opportunity loss and emotional damage.

No one can answer this without reading your contract. So your lawyer is better than an internet message board. General rule of thumb is that exterior square feet are valued at 50% of interior square feet (could be less with a high ratio of outdoor:indoor sqft). With your contract price and an excel sheet you could get to the right number for a credit, or at least a number you could start a negotiation with.

What does the contract say?

Long story short, the listing (on SE) showed the terrace being attached and during the tour, I was shown the private terrace too. However when my offer got accepted and the offering plan came, I did not see the terrace included. My lawyer sent an amendment over to the Sponsor and they DID try to give me exclusive rights. However, the terrace was not filed with the building department as a finished terrace space and would require completely refilling the certificate of occupancy, which the sponsor was not willing to do., hence they offered me $15,000 credit (equates to $ 37 per square foot...)

Language of the contract for the amendment is below

"Sponsor agrees that the closing of this transaction is subject to Sponsor filing and receiving
approval from the New York State Attorney General’s Office (“AG’s Office”) an
Amendment to the Offering Plan for the Condominium (the “Amendment”) which will
amend the description of Unit PHA to include as a Limited Common Element, a private
roof terrace located on the roof of the Building, the exclusive use of which will be that of
the owner of Unit PHA and be governed by the By-Laws as a Limited Common Element.
Should the Amendment not be approved by the AG’s Office by the Closing Date as set
forth in the Purchase Agreement, the Closing Date shall be adjourned until said
Amendment has been approved by the AG’s Office, at which time, Sponsor shall provide
Purchaser with no less than ten (10) days’ notice of the rescheduled Closing Date."

Thank you

As many have noted, a lot depends on what the contract says. Contracts are several pages for this purpose, like a prenup, a litany of provisions in case of a divorce.

That aside, if you wish to(or can) proceed with a discounted amount, do not forget about the extra shares and therefore extra maintenance cost (and later unabated taxes) this unit has and include a remedy or dollar figure for that.
This will likely be quite ugly as all the documents for the abatement, for the declaration, etc may be just as cost prohibitive as refiling the C of O.
I'd bet the extra shares , and therefore extra maintenance (and future unabated taxes) is a minimum 15% over a like kind unit without the outdoor space.

Very tough situation.

for the inconvenience, the credit should be at least $1500/sqft

Get your money back and move on... Your life will be better for just not having to think about these jokers every again.

Sorry didnt read the amendment.

Honestly, its not that terrible. Your not losing the terrace.
Its something to discuss with your lawyer to explain exactly how your rights are diminished here in every possible aspect.
Along with the $15K, if the building keeps responsibility for maintenance and repair of the terrace while you have exclusive right to it, its not the worst thing either.
Or the building could give the unit an ironclad 200 year lease for the terrace at $10.00 per year rent.

@Truthskr10 The Amendment was REJECTED (so I am losing the terrace) due to "terrace was not filed with the building department as a finished terrace space and would require completely refilling the certificate of occupancy". In other words the terrace above the PHA cannot be used by ANYONE (wasted space).

I suggested to my lawyer a clause saying if the Department of Building decides to make the terrace a recreational space, it will be deemed exclusively a license to the #PHA - so they can't screw me over in the future if they do make any changes....

I also pointed out that they are valuing the terrace less than the square foot per dollar then properties in Flint Michigan (https://www.zillow.com/homedetails/3506-Brentwood-Dr-Flint-MI-48503/73932549_zpid/) 70 dollars per square foot.

So I just read the condo declaration.
Page 17 addresses Limited Common Elements
Paragraph B subparagraph (c)
Balconies and private roof terraces
The entrances to any limited common elements are maintained by the building,
every other aspect (the terrace) is to be repaired and maintained by the individual.

Here's the rub;
PHB and PHC roof terraces are already listed as limited common elements.
PHA does not show a roof terrace which the posted amendment will cure, however you should know that all the balconies including PHA are designate "limited common element" AS WELL.
page 27 of the condo dec

The only thing wrong here is your roof terrace was omitted from the original condo dec

If you really like the apt take the $15K for the time and suffering, this unit with the amendment is on equal footing to the others in the building.

But do please confirm all my info with your lawyer.

I am not an attorney but I play one on TV :)

@truthskr10 Wow thank you for going through all of that...you really didn't have to!

But thank you again!

If I could only figure out how to get off Streeteasy's naughty ("new to street easy talk" - although I've been posting for 3 months) list my previous post will seem redundant...

Thanks, at this point, it's going to be, "Do I think this apartment will be worth it".

You may well be SOL. The wording of the contract seems to say that it can't close unless and until the govt does something (a "condition precedent"). If the govt doesn't do that, you have a contract that can't close. If the sponsor refuses to refund the deposit, you might sue on that basis, but good luck collecting for emotional distress and the rest. You signed a deal with an unusual condition precedent, and you lost. Sorry.

BTW, a better lawyer might have added, "Should Sponsor fail to secure the required approval by [date], Buyer may may, at his sole option, (a) declare this Agreement null and void, shall be refunded all Earnest Money, and may demand an additional $20k liquidated damages, or (b) demand that the purchase price be adjusted to $x."

If sponsor wouldn't agree to that, you would have known that they were full of sh!t right from the start.

Without being an expert, sponsors are on a much tighter leash than other sellers and more likely to give the deposit back rather than stuck with a contract they can’t close on.

Just sue them