Buy home to fix up, then sell back to original owner - best way?

[Jason Munger]

Home is vacant, 100% equity and needs a LOT of work

I'm looking to house hack and live in the home while I fix it up.  Then 1-2 years down the road put it up for sale.  Ideally I would like to sell it back to the current owner (long story, they can't afford the rehab themselves).

What would be some best ways to structure this deal?

Ballpark numbers, just so the conversation is easier.

Current value: $75k
Repair costs: $125k
ARV: $300k

*I would do a lot of the work myself

I want to be the "home owner" throughout the project for the various reasons, including have financial security that I'm not dumping a ton of $$$ into someone else's home.  Plus there is no guarantee that they will be able to (or want to) purchase the home when I'm done.  Also, I could claim homestead on it and change the insurance policy to owner occupied/primary residence and save a lot of money there.

On the flip side, that requires two closings and also risks losing some grace on current building codes that the home is currently "grandfathered" for.  OLD home.