How to structure a investor partnership?

[Paul Martin]

I have an offer in on what appears to be a very good commercial deal that I'm getting at a solid discount and would like to fix up some, fill 1 of the 3 spaces available (after a rehab) and put back on the market, fully leased. Buying it for $650k (currently  listed for $890k—I'd rather not discuss why it's a firesale, lets just go with those numbers), expecting to put in up to $215k ($162,500 DP and $50k rehab) and get it back on the market for $1,000,000, ideally within 6 mos.  That leaves me with around $300k profit. 

My question is this: I've been investing awhile and have had success with 10% interest only loans from business partners. One of these guys would prefer a limited partnership on our next deal. So if I was to partner with him—essentially giving him access to all the numbers—what's an appropriate deal for him? If he were to loan me $100k at 10% interest only over 6 mos that's $5k, relative peanuts with regard to this deal. Would just offering him 10% of net proceeds—giving him $30k instead of $5k—be insulting? I would like to do the right thing by both of us. 

Of course if it sits for 2 years before selling gives him $20k... Lots of factors but on the 6 month version, any advice?