The biggest savings are for a recent documented reroof up to current code and then clips for roof to wall connections.  

Then you have to deal with the coding of whatever state/city you are in. 

I had worked part time as a framing carpenter on my holidays and had helped build family members houses, so I had enough ideas to be dangerous, I demolished a non compliant addition to the house and rebuilt it to code on the same foundation.

Can you kindly let me know which ZIP codes are best for the Children's Hospital workers?

@Alan Le  just do it to code.

I called the Montgomery County Licensing and Registration office with my questions and they told me to just "look online" for the regulations, so here is what I found:Class 3 ADU Requirements (last updated 3/4/2020 after the new ADU law in MoCo passed)2020 MoCo Housing Code Enforcement GuideIn the Housing Code Enforcement Guide, it states room length and width requirements for "minimum dwelling standards" and "habitable space."

There are videos on youtube that can help you find hot markets in your area based on home sales within zip codes. 

Purchase price: $40,000 Cash invested: $20,000 Address: 2420 County Road 432City: RockdaleState: TXZip Code: 76567County: Milam County Subdivision: J J Acosta Surv AbsLegal Description: A0010 ACOSTA, JUAN JOSE,5.95 ACRESBuilding Sqft.: 952 /Appraisal District Year Built: 2010 /Appraisal DistrictLot Size: 259,182 Sqft.

They will help you navigate the permiting proccess and getting the unit up to code.

Code Sec. 5.066, the seller or landlord must give a 60-day notice of default and opportunity to cure the default.