I'm going to go out with a professional inspector to go over the major items and check permits since the square footage is not as listed with the property appraiser.

I've always found it a bit more difficult finding a solid GC that can take on a project where adding square footage is part of the game plan.

Comparable sales, square footage, beds, baths, garage, pool, and several other factors will come into play before appliances.

As far as I can see, they see all closed sales in your area, come up with an average price per sq ft and do a simple math with your sq footage.

Other homes in the area either had too few rooms, not enough square footage, too far away, and not within the past 6 months.

what's the sq footage?

I would have each unit pay based on their proportion of square footage.

You're looking at about $20k per unit total for the same square footage.

Penalties and loss of rent / discounted by square footage loss of use by tenant,, does not make it a win for working in a occupied unit.This alone would give me pause to consider letting tenant stay.. 

Same with square footage, if you have more sq foot than everyone else, then you won't get the total cost to cure.