300k to build 1100 SF 3/2 ADU or invest in stock market

[Victor Latimer]

Hello all. So I live in the south bay of Los Angeles (Torrance/Harbor Gateway). My primary property is a 3/2 1266 SF home on a 7500 lot. We have in a hand the permit to build a 3/2 1100 SF home in backyard. I I can get the build done for 275k. This is a very reasonable price. And yes it's legit. The upside would be passive income in the range of $3500mo. Not sure about the added value to overall property since this is relatively new. Of course the new bill allowing us to possibly sell off either property is enticing but not sure how to value that either. The down side would be having tenants in our backyard along with all of the other potential landlord headaches. We have a duplex and a lake townhouse that we rent long and short-term out of state so we have some experience as landlords. Now I just want to ask any of you out there would you build in my position or invest that same amount of money? They both have have uncertainties. I'm enticed by stock market as I believe AI will likely make for greater returns in future due to companies running more efficiently. Assuming I could get ROI of 10% over 20 years investing in the market, what would you do?