Adding An Extra Floor to a Condo Top Floor Unit

We live in a small condo, just 8 units and self-managed. All units are owned except for one. The sponsor still retains the top front unit, and the roof rights above the unit (it has a private roof deck). Our area just saw a change in FAR, which means the building can build higher. The sponsor wants to now build an extra floor, turning his roof deck into an extra bedroom. The building/board is... [more]

We live in a small condo, just 8 units and self-managed. All units are owned except for one. The sponsor still retains the top front unit, and the roof rights above the unit (it has a private roof deck). Our area just saw a change in FAR, which means the building can build higher. The sponsor wants to now build an extra floor, turning his roof deck into an extra bedroom. The building/board is generaly fine with the arrangement. The sponsor is happy to sign an alteration agreement, provide work hours/schedule, pay a deposit and provide construction docs and sign-offs by architect/engineer and file his plans with DOB. The concern we have is what the bulding needs to do to make this 'official'. We assume we need to make an alteration to the layouts in the offering plan and reapportion the common charges (not complicated in concept), but do not know what this truly involves. We are concerned with unnecessary or inflated legal expenses for something we feel should be straightforward. Has anyone out there gone through a simlar situation in NYC? I'd be grateful for any advice or information on the process and what the potential costs can be to do what is necessary. Any and all advice appreciated - [less]