Sorry to hear of such an unfortunate situation. Were you represented by your own agent or the Builder's listing agent? Builder and his agent(s) should have given all necessary dsiclosures in re to the status of the conversion. When you wrote the offer had your agent provided you with a number of disclosures which strongly encouraged you to do your own independed property inspections and investigations, including permits, to satisfy your knowledge of what you were purchasing. Before calling an atty gather and read all documents and disclsoures you were provided with during Escrow so you can have a fresh understanding of what you signed. Next I suggest to contact the Title Co insuring the property and talk to the Title Officer, they should help you. This is a problem for them as well. If they are not assisting you in resolving this, contact a real estate atty.
I hope you'll be able to have this issue resolved quickly and at no expense to you, so you can enjoy the place and being a home owner.
DRE lic # 1335053
2010 Top 8% Producer
Diamond Society Award