Since you can't say for sure what will happen, you should plan for the worst case scenario (fully demo the illegal unit).

And, if I was to assume an extra $20K-$30K of additional costs for any flip that requires significant demo work, then that would really kill most deals. 

The demo on the property has been completed and we're ready to start installation.Thanks

Woburn MA - 2/27 630pm - Networking, sharing my story, and calculation demo - https://www.biggerpockets.com/forums/521/topics/805189-pints-properties-and-events-new-englandLowell MA - 3/12 630pm - Networking, with member to be named and guest speaking -https://www.biggerpockets.com/forums/521/topics/807025-pints-properties-and-events-new-englandSalem MA - 3/19 630pm - Networking and sharing local market knowledge - https://www.biggerpockets.com/forums/521/topics/808843-pints-properties-and-events-new-englandBest, Jon

He already did all the hard stuff: demo, new roof, new electric and plumbing, new custom windows, drywall.

Please visit the CHBO website and reach out to setup a demo of our services.

I notice that on wholesaling calculator on this BP, there are section for "estimated repair cost" and under that section, it has Exterior Repairs: Roof, Concrete, Gutters/Soffit/Fascia, Garage, Siding, Landscaping, Exterior Painting, Septic, Decks/Porches, FoundationInterior Repairs: Demo, Sheetrock, Plumbing, Carpentry, Electrical, Interior Painting, HVAC, Cabinets/Countertops, Framing, Flooring, InsulationGeneral Components: Permits, Termites, Mold, MiscellaneousWould this be good enough (complete) list in which I can represent this list with (columns of labor and material costs) to the general contractor and be assured that I would be able to get a good ballpark precise range of estimated repair value that would be valuable to the end buyer/flipper? 

Unfortunately my demo crew threw away all the baseboard heater covers.

The home is vacant now and just completed demoing the inside as it was un livable.  

The cost in doing so was pretty nominal (demo two closets & build two walls), but I think it adds tremendous value and appeal to the property.