any building materials you can get free that are scrap or cheap?

We did have to put a new furnace in (it hadn't had a working furnace in two plus years) but beyond the one end of the house, it's mainly cosmetic. 

The GC there hired hired a kid to basically sit and watch the vehice and materials all day every day so no one would steal.

Update: after several weeks of silence I told the seller I was still interested long story short they accepted the offer I did an inspection and there's black mold in the attic, some electrical work, mold in all the windows, not properly vented attic, bathroom mold, needs new carpet and cosmetic stuff.

We pick material, finishings... make the house flow (people like open concept now so we move walls where we can, etc). 

We have a few from overseas that have a tax requirement of showing material costs on larger items (furnace, hot water tank, windows, roof etc) so we send them material receipts.  

If you are considering an prefab ADU, take a look at the prefab options with Back Porch Homes, they are prefab stick built homes and all materials used can be replaced/repaired with products you can find at your favorite hardware store instead of specialty stores like more manufactured homes.

You arent taking into consideration rising lumber and materials costs , contractors are busy and wont get to your job for a month or two .

I can come back in person for only a few weeks out of the year (gotta stay tax exempt), so basically one big trip home each year or so.I've got some good reading material for tonight, and hopefully I can find a few hours of stable connection tomorrow as well. 

I do not possess the creativity when it comes to home design to decide how I want the kitchen or bathroom to look and what materials I want to use.