Well..With a private lender, you're going to have quite a bit of flexibility. Everything is negotiable here...If you want him to partner up with you, he can put up the money, you manage the deal..split it 50/50.
If you want him to act as a hard money lender typically a HML will lend up to 70% ARV (after repaired value). This means that a hard money lender can loan you up to 70% of what the home is worth in repaired condition.
So if you find a home worth $45,000 in the condition it's in, and needs $20,000 in repair work, and after it is repaired the current fair market value is worth $100,000, then typically they can lend you up to $70,000, which would cover the cost of the house and the repairs.
Because he's a private guy, you can expect a little higher interest rates. Interest rates vary from 12% - 20% (I'd try to stay closer to the 10 - 12% area if possible). I wouldn't use hard money for more than 4 months.
Typically hard money lenders will charge anywhere from 2-10 points just to use their money.
(One point equals one percent of the mortgage amount. So charging 1 point on a $100,000 loan would be $1000.)
Other things to consider are how quickly funds will be available. You need to make sure that this guy can act fast. I've seen some B.S'ers in my day that talk a good talk, but when it comes time to cutting a check, they want to ANALYZE EVER ASPECT OF THE DEAL and kill it.
Best of luck,
Rich
Ps - Avoid pre-payment penalties.