For example, a Smartthings hub with various sensors that would alert me immediately to water leaks, temperature extremes, frequency of furnace filter changes, and access gained to off-limit areas to name a few that come quickly to mind.The problem is that I really don't want the expense of providing internet & wifi, which would leave the renter's wifi as the only way to connect.  

Being flexible (considering warehouse conversions, facilities that are "too" small but with room to expand, etc) will increase the supply available to you.

The contractor should have known better than to use thin rock that would move under stress of walking, expansion and contraction of temperature. 

The Heat Ordinance mandates that during cold weather months landlords supply heat to rental units or to any unit where owners do not have individual control of the heat.From September 15 through June 1, the temperature inside a rental residence is required to be at least 68 degrees from 8:30 AM to 10:30 PM, and at least 66 degrees from 10:30 PM to 8:30 AM.Landlords face fines of up to $500 per day, per violation, for each day they do not supply adequate heat.

I can see how your tenants would be especially happy about being able to control the temperature. 

Warehouses and fulfillment centers? 

Forest lands are one of the more passive and treated me good all these yearscheck out this website http://northwestforestproperties.com/oregon-forest-land-sale/blue-river-tree-farm-east-4200001/ going to south America or Central America in search of exotic timber is only applicable to a multi billion dollar corporation .Warehouser tried this in Siberia and promptly lost about 1 B within 24 months.. and left ...look no farther than the good Ole US of A for these types of investments.there is a reason the number one and number two owners and financers of US timber lands are John Hancockand the Harvard endowment fund..

Another thing to consider is that windows are a major source of temperature loss and sun can heat up the property through the windows.

If you want to stick to real estate, there was even a guy there that buys vacant land in California, builds these giant warehouses, and rents them to marijuana growers, distributors, manufactures, etc.

The A/C deal as to temperature in the unit is probably a Habitability issue so if you need to do a quick fix and get some window units to cure the problem do that.