Who's carrying the note and risks associated with potential budget (time and money) overages? What's the profit split? What about the cost of standard 1 yr warranty repairs, call-backs, etc.?
I had the opportunity to invest in a similar deal my builder wanted to do as he was debt constrained with his lenders on spec homes and couldn't put any more homes into production. My spidey senses went off as he wanted me to sign a purchase contract (affecting my DTI, I'm fully on the hook to buy if we don't have a buyer, etc.) that would allow the bank to lend him the money for acquisition, construction, etc.
I had no problem putting the 10% down to secure financing. But no way I touch a promissory note and cash deal for anything less than 60% of pre-tax profits. He wanted to give me 30-40%. Thankfully I paid attention to my gut and walked away. Would have broken ground right before the stupidity of supply chain issues and material cost increases...
But you can make damn good money doing it. Just don't put all your eggs in one basket and have as iron-clad of an "out" as you can manage.
Amateur pro-tip: never, ever, ever, ever personally sign for these types of loans/deals. Put it in an LLC or something. Never in your name. Ever.