Some stuff you can get an "estimate" for from a GC just off the square footage. 

What square footage is the commercial space?

More bathrooms, square footage, yard, hardscape, fence has more costs than less.  

Building will be 80k-200k depending on size and square footage.

A super ball number to get you going would be at least $190/SF-$220/sf ish... to figure out square footage it's probably best to connect with a Chicago architect like @Samuel Pavlovcik or @Prashanth Mahakali both can talk through the zoning and plan development process.

I guessed (admit I did not look up) an average for a SFH because we do not know br, ba, footage.  

Seems renovating this part of the attic would require ceiling insulation, drywall, flooring, electrical outlets, & heating source.My concern is that a reappraisal wouldn't add anything to legal square footage. 

So increased sq footage with a 3/1 should do well.  

., hours committed to representation, achievement goals, discounts for properties based on price for square footage, negotiation of post escrow discounts, credit for seller/agent cooperation, transaction coordination commitment) might be more digestible for a buyer.Should be interesting to see going forward, but I do think in general, agent compensation will be less as things develop.

Saw value in location and sq footage.