So all you need to do is start getting your contractors lined up and scheduled to be onsite the day after you close (or earliest possible day) to begin your demo and then re-construction of the property. 

I have had 4 knee reconstructions in just over 18 months, so have basically been unable to get around like I once could.

Under 425 ILCS 60/3:(f) In the case of any dwelling unit that is newly constructed, reconstructed, or substantially remodelled after December 31, 1987, the requirements of this Section shall apply beginning on the first day of occupancy of the dwelling unit after such construction, reconstruction or substantial remodelling.

Unit of comparison could be per door (unit), per Sf, or total property, etc.Not sure if the balance of value between MF and the commercial building but if I couldn't find similar sales I would probably use a combination of both MF and commercial comps- assuming a retail or office space.Income Approach- appraiser will reconstruct the operating statement from market data and then will develop and opinion of the NOI and overall cap rate.

Just curious in the process of doing these reconstruction flips.

When it comes to reconstruction /replacement  I would appreciate advice from those who know. 

Qualified acquisition costs mean the costs of acquiring, constructing, or reconstructing a residence, including any usual or reasonable settlement, financing, or other closing costs.

Should he re-construct it back to its original plans?

If you lose money, reconstruct and try again.Find a REAL GOOD real estate attorney.  

If you're planning on doing flips just beware because a lot of the older homes are more in isolated areas and even when reconstructing a home most families will want to live in a subdivision for the amenities.