One way that you can structure it is to form an LLC with this person and then form a bank account under the LLC that they deposit money into and you pull from.

If listed with a broker they may have a pro forma that they could provide. 

I would recommend modeling vacancy into your pro-forma (maybe 8%). 

@Ty Jarnagin Ty, a good business plan starts with a good pro forma that analyzes and reports financial performance on a project and stakeholder level.The business plan should be based on pro forma snapshots that support the narrative you create to tell the project’s story.The story needs to include total project cost, capital stack, how equity capital is apportioned and profit is shared between the sponsor and investors.All of the above needs to be set and referenced by time which is used to calculate partnership funding obligations and the returns generated to the project and its stakeholders.

Would you searchsomething form a wholesaler?

Any ol' programmer or business kid used to be able to form a start up and get it funded and use this is afford expensive housing and hire those who can.

This one with my pro forma calculations has a $200/ month cash flow so I can see why it's may have a tougher time moving. 

There are only 3 reasons to form a partnership. 

Since it would take 12 to 36 months to build the property anyway you might be able to get a lender to finance based off of the pro forma value of the after completed duplex at a substantial rent premium to whatever your underwriting today.As mentioned about $96 psf cost to build seems wildly low considering the market supply issues on materials and inflated demand do to low cost of capital and now congressional fiscal stimulus and tax programs.

At least now you know how the whole process of buying a property looks like and that closing costs are a lot more than what Roofstock assumes in their pro forma calculation.