Much of real estate investing is being able to sleep at night and I imagine that's very difficult to do if you're worrying about if your $X00,000 beach house still has a roof the day after a Cat 5 blew threw and a Cat 3 pending the following week.   

The second one needed a full roof.

People are often lax when it comes to their revolving credit but not with the roof over their head.

or “Is it legal to build a treehouse on a duplex roof?”

Anything above that needs to be justified - roof replacement, parking lot repaving, etc. 

I saw an ad for EverSeal offering a 50-year warranty for their flat roof system.

I would suggest just that, house hack a 4plex for cash flow, and save for your second creative finance deal and grow from there.The idea here is you should be paying zero for your roof (or close to) before buying a second property.

Quote from @KiKi Wood: Personally, I would say that anything more than ~22% is a little steep...Hey Kiki,Thanks for your thoughts and I think everyone is entitled to their opinion.

We did notice some water damage in the front of the house but was told the roof is in good condition.

I’m in the learning stage of starting up and it is a steep learning curve with tons of information to digest.