Then any rental income you could obtain from that property could be used as an income source for loan pre-qualification.

Will he and potential buyer of the property be subject to Commercial financing or will the property still qualify for residential 4 unit and under loan types/primary?

Would a HELOC or home equity loan on my personal home be a good idea to fund this?  

The terms for a 2nd position loan on a rental is 6%, 25 year term,  and 2 points origination fee.  

DIRECT MORTGAGE LOAN COMPANY6.

The deal will leave the seller at your sons mercy for decades (the life of the loan).

Lenders are lining up to provide down payment, “gap” financing, and earnest money deposit financing so that they, with no experience, no capital, and no knowledge can purchase a property they incorrectly analyzed as a good purchase, for “nothing” down. lol, if you need a loan for the earnest money, you are not ready to invest.

(Either with the roofing company, a heloc, or a personal loan.)Either way you will probably be way ahead on interest saved unless you have a sub 6% interest rate.

It super easy you sign up to have a quick call and do a quick tutorial with a Rep and you receive a certificate that you give to the Banker/Loan officer.

Hey Mario, We're doing several rehab loans right now...mainly in Pinellas...on Hurricane Milton-damaged homes.