Some of your costs will be property taxes, maintenance, insurance, debt service if you get a loan, CapEx (replacing items such as roofs, AC systems, etc), vacancies, etc.

I own a townhouse near Boston, and there is a leak in the roof caused by an ice dam. 

When it is time for a roof, you have 4 units to spread the costs over.Good Luck

I own a condo in a building that needs about between $30,000-$40,000 for some work done on our roof.

There are no leaks in the roof, however, it appears to be about 15 years old. 

Ive used hard money and conventional financing in the past; however this one has numbers that wont work for those and was wondering if there was an option to create a win-win for everyone.The home is currently valued at $70k conservatively and is in clean condition (just an older roof). 

Other than a new roof that was 50 squares it has been very low maintenance, so while cash low is low, cash on cash looks impressive. 

You might structure your interest with a note.If you are in title, you will be on the security agreement, deed of trust, but you may stay off the note.Frankly, I don't mind personal liability issues with rentals, good management keeps me from being negligent and in any event someone chases me, I'll sick my pit bull insurance agent and company on them, no one here will get past the liability limits even if 20 kids fall off the roof or the place blows up.

If you go with 2 SFRs rather than a duplex, you have two roofs, two furnaces, two hot water heaters, two driveways, etc, etc.But you have advantages.  

In my case the above mentioned properties ten years later close to doubled in value and the rent went up about 80% and now 15 years later FMV  tripled and rent is doubled and now the same house cash-flows about $800-$1000 per months EACH even with an occasional furnace/roof replacement.