don't make a federal case out of it

First, waived deductible is questionable in ethics and probably violate insurance contract. But I won't comment on it further.  天知地知你知我知。

Second, the waived deducitble is treated as cancelled debt by your roofer towards you.

If the cancelled debt (waived amount) was more than $600, the roofer would be required to send you (and IRS) a 1099-A, and you have to report it as the income of your rental property.

But since the cancelled debt is only 300, neither you nor the roofer needs to report.