There's no exact science to it but like you said it's only usable about half the year (due to temperature, I presume) and then even when the weather is warm, it could be raining, so truly only available likely somewhat less than half the year - maybe an extra $0.15 - $0.20 psf/mo added to the $1 psf/mo sounds reasonable.

Available lines of credit and a steady stream of extra money from your w2 job can’t mitigate that risk .

Dirty, needs some major cleaning on the inside.I'm happy with collecting passive income and having a steady paying tenant. 

I'm too skeptical for some things thought.... 1st I have no numbers in my hands since the seller never involved in renting the apts , 2nd Do you think I'm exposed to a bigger risk since it is the beginning and I will not have a steady cash flow out of short-term renting? 

Slow and steady has worked well...no regrets.

Real estate is a “get rich slow” scheme.Slow and steady wins the race.I did not buy my personal residence until I had 25 units.

The reason you see agents driving new cars and wearing bling is because the majority of them have already retired from a previous career or are married to someone providing a steady paycheck.I have 160 agents in my market.

A steady clientele?

NOT a steady state area with little rent or price appreciation.  

With the high construction costs nowadays it's hard to add that much value, plus ADU's don't sell at the same $/sqft as the regular house, and there's not a steady readily available comparable properties to base valuation so the easiest method is replacement cost.I hosted a Meetup and wrote about ADU's on my website.