Any investor-friendly (good pricing, contractor cash accounts with discounted pricing, etc) supplier recommendations for various materials (flooring, tile, stone, countertop materials, hardscaping, lumber, windows, fixtures, roofing materials, etc) is greatly appreciated!

Depends on when he bought the lumber of course. 

But not only is that hard to do normally, it's nearly impossible these days with shortages and huge price hikes on key building elements, including lumber and labor.

They may be able to adjust the sale price based on increased materials costs such as lumber.

It’s also hard to find decent labor now because contractors are slammed, and nobody wants to work, plus lumber costs.

My thought process: Cap rate is pretty low at 3.2% and I feel like appreciation will slow considerably and potentially correct as interest rates eventually rise, lumber costs decline for new builds, and homeowners start selling as covid fears subside.

I'm seeing more off market stuff as local Mom and Pop investors want to unload their portfolios. 

Fast forward 18 months and now lumber has tripled and the $150k I had budgeted to build won't be enough.

I wont lie....half of it is a dump outside full of cut lumber and shrubbery.

It could be an intentional deception to cover up trouble tenants and unload a problem on a buyer.