That window may not have been installed properly.

Would fabricated or manufactured housing count as an ADU to build, rent and possibly sell under this new law? 

The rest "should be" (if bought properly), paid for by someone or something else. 

Take ownership of your mistake and learn to do the proper due diligence recommended above😊

If so, make sure agreement is in writing, signed by both parties, specifies new end date and ensures any existing security deposit will still be dealt with properly per landlord/tenant laws, and I'd also ask for a partial payment to be issued at signing to make obtaining his new place easier.  

For newly constructed, purchased or renovated properties and also retroactive generally over the last 10 years, building components are properly classified into individual units of property and accurate recovery periods for computing depreciation deductions.

Also, I have all the info on the mobile homes Manufacturer, year, model numbers, beds, baths length, width as well as what was paid for each unit.

They also do not have a proper screening process for tenants.

I've helped a few people with considering modular rebuilds in fire areas and there are some modular and manufactured companies that I work with with that have some specialization in the area. - Orbit is one.

@Rahel KetemaI work in the commercial HVAC world as a salesman for a major manufacturer in the US and I have sold many residential furnace splits and ductless split systems in NJ/NYC, so temp wise similar to Chicago.Everyone has provided some good points and some to ponder.The upfront cost is going to vary based on the heat load of your space and the layout.