I am not sure I fully understand your proposal.  I understand the “donor” buying the property and renting it to you. I don’t find such deals particularly attractive if there is an alternative because they so frequently make the property subject to real estate tax.  In most states, property owned by an individual or a business would be taxable when the same property would be exempt from real estate tax if owned and used by the charity. The charity also pays out a lot of rent over the years and ends up with nothing of value at the end of the lease.

I understand the donor lending you the money and taking back a mortgage.  Assuming you can afford it, the lender would obtain a return on his money and you would end up owning the property when the mortgage is paid off. You probably avoid the real estate tax along the way. (Of course, if you use the property for unrelated purposes, you may have to pay both real estate taxes and unrelated business income tax on debt financed property.)

I also understand the donor contributing the money to you so that you can buy the property and he can take a charitable contribution deduction.

I don’t understand his making a “donation” and getting a royalty in return. That isn’t a deductible contribution and sounds much more like a mortgage with a very variable rate. The IRS generally does not like percentage arrangements based on a percentage of profit or surplus, but accepts percentage arrangements based on gross revenues. I don’t know why a percentage payment based on gross revenue from the property would be impermissible, assuming that it is reasonable under the circumstances. But I don’t understand exactly how it would work and how the IRS would characterize it.  If you hope to use it to get a good deal from your donor, perhaps you can negotiate a partial gift and partial loan with a regular mortgage. It would be more understandable to the IRS and everyone would get something clear as an immediate benefit.