Cheapest is treated lumber (6x6), then metal window wells and then stacked retaining wall block. 

This is a 4000 sf two story property in Florida, with a steep metal roof, so they have to bring out a cherry-picker.  

As far as insurance, I'm not certain how much your regular homeowner's insurance would cover in an STR situation (although honestly I'd be surprised if that negated the contract), but Airbnb holds $1M in liability on your property, and an additional $1M in property and bodily harm.

Additional labor costs should be expected for any set up like cement floating or installation of hardi backer (cement board, etc) as well as additional labor costs for intricate layouts or details like metal edging or bull nosing stone. 

If you can afford it, metal roof will last well, won’t catch fire, great with snow. 

I've had similar thoughts about metal roofs as they are more unique and provide an advantage in durability.

If I change a ceiling fan or a light in the ceiling, the screws and metal box are so hot I can barely touch it. 

My contractor has installed both and thinks that the only difference between 2500 & 4500 is a metal strip along the bottom, which he finds unnecessary for all but wide windows.

I currently am working in the scrap metal industry in a job I love, but 6 days a week and usually almost 70 hours a week doesn't leave much time at the end of the week.  

@Roman RytovIndustrial buildings in the southeast is the only class I invest in.Is it a pre-engineered metal building or block and bar joist type structure?