Added a bathroom, making it a 2/2, then opened it up to less qualified buyers by offering financing.What was the outcome?

They have good network of contractors that give discounts to members too I believe. 

I am currently working on building a 480sqft 1 bedroom, 1 bathroom unit in the backyard of a rental property.

An off-market deal takes longer to find but has the best chance for attractive discounts. 

A single piece, arched up  at the back wall and tilted downward towards the doors so any water runs out onto the kitchen floor vs under the cabinet.That way the renter must notice water vs. just letting it run under the cabinets until it ruins the ceiling downstairs.Make sure to glue the edges with bathroom caulk. https://www.homedepot.com/p/Everbilt-29-in-x-33-in-Low-Profile-Washing-Machine-Drain-Pan-in-White-98244/307638946Hmmmm, maybe I'll write a book on how to harden rental units for pets and other damage.Also, since the renter has been in there for 6 years, you should have the dryer vents checked for lint buildup.This is recommended to do once a year.  

Same goes with walls/bathroom/etc. and over time I’ll be able to see a property and have some form of idea about rehab cost.

There is obvious water damage on the ceiling and near the shower and the bathroom the floor below.

HOWEVER, small multifamily properties here (and probably everywhere) incur a "plex discount" with tenants and that is a bummer. 

We're just adding a kitchen, closing off a hallway, and changing an entrance to a bathroom.

Adding a bathroom and creating parking.