I am also interested in purchasing a large industrial building to rent out indoor RV and Boat parking.

In Cosby properties on Cosby Creek and in Maranatha Resort (where all the existing cabins have indoor pools) tend to be the highest producing rentals. 

If you use a bit of imagination then you can work wonders with shipping containers with some fascinating architectural features, like atriums and tall indoor waterfalls.

Per my understanding, that means a 2400 sq ft lot would allow at most 2160 sq ft of finished, above grade indoor space. 

California has specific mold laws - I suggest you read up on themCalifornia's "Toxic Mold Protection Act of 2001" authorizes the state's Department of Health Services (now called the Department of Health Care Services) to set permissible levels of indoor mold exposure for sensitive populations (like children, or people with compromised immune systems or respiratory problems).

Starting with, Roughly 18 Years as a Mason,Concrete Finisher, general Contractor/ Indoor & Outdoor,Landscaping ,Tile Work, Dry-wall, Kitchen & Bath, Paint, Etc.

Most of Iowa is in Zone 1, which the EPA states has the "Highest Potential" for radon: Zone 1 counties have a predicted average indoor radon screening level greater than 4 pCi/L (picocuries per liter) (red zones) A basic radon test can be picked up from your local hardware store with results usually only taking a couple of days to come back.

Heating costs go up in winter, as does electric due to the reduced natural light and people being indoors more.

I've seen many garage conversions where having that big roll up door (depending on the style) is actually a bonus because it can open up the living space to a patio or yard and people like that indoor/outdoor feel, especially in So Cal.

We agree that they take the trash out, they don't park in the front yard, they don't put indoor furniture on the front porch, and they don't let any stray animals inside.