My plan is to place a reflective thermal barrier on top of the existing cool coat roof, then add 2 x 4 furring strips for the needed air gap and then 26 gauge sheet metal roof overhanging the eaves by 12" so rain will run off the side away from house, not down the side of the house. 

They've complained about the upstairs bedrooms being hot and minimal air flow. 

View a few units to see what the standard is for the area: stove, dishwasher, range, forced air, boiler, etc.  

The unit itself is only three years old.Sooo I decided to spring for all new ductwork and vents - they also widened the tiny 2 x 12 vents in the larger rooms for better air flow - it took two full days and cost $3900 for a 1600 sq. ft. house.

I don't deal with the air b and b things much but I believe that status has tax implications too. 

Renting out bedrooms as an air bnb might be over-whelming based on what others have said here.

These sites have very generic and do not take into consideration things like, building codes, zoning requirements, light and air requirements, site orientation, utilities, soil capacity for foundation types, etc.

central valley up to Lake co.. look between Redding and Woodland etc etc there are plenty of places you can buy that will cash flow.. without going all the way across the country.. you could look at student rentals.. you could do air bnb in a place like Portola  Greagle  plenty of places to buy in CA.

The problem is steam pushes out the air through the radiator vents and vents on the mains.

That's also why I put air quotes around "hidden" because if you actually look at the leases this can be missed.