If the entity produces passive income such as rentals or interest, then there is no generation of Unrelated Business Taxable Income.If, however, the entity is engaging in a services business or something similar, perhaps hotels, self-storage, adult care, etc., then that produces trade or business income.  

Commercials properties, lease options, single fam, multi f, storage unit, whole life insurance (be your own bank), small business(ice cream shop), airbnb,etc...

“The gross building areais the total finished area including any interior common areas, such as stairways and hallways of the improvements based on exterior measurements;is the most common comparison for two- to four-unit properties;must be consistently developed for the subject property and all comparables used in the appraisal;must include all finished above-grade and below-grade living areas, counting all interior common areas such as stairways, hallways, storage rooms; andcannot count exterior common areas, such as open stairways.Fannie Mae will accept the use of other comparisons for two- to four-unit properties, such as the total above-grade and below-grade areas discussed in Gross Living Area, provided the appraiserexplains the reasons he or she did not use a gross building area comparison, andclearly describes the comparisons that were made.”The actual form utilized, in this case Form 1025, does not in any way dictate what is proper and appropriate in the completion and reporting of the appraisal.

I recently had a tenant put a charcoal grill in their attached storage closet with hot coals still present - which ofcourse resulted in carbon monoxide filling the closet, and then the house.

Or a self storage facility with an owners quarters. 

I was recently able to close on 2.5 acres of properly zoned land to establish an RV/Boat storage facility on.

Costs of building solar and wind projects are at record lows and solar plus battery storage is now more competitive than fossil fuel generation. 

There are many niche areas but I favor MF apartments as a core REI syndication holding as well as diversification into self storage and mobile home parks as well may be an option. 

Some appraisers view closets, stairways, storage areas, enclosed patios, and other spaces differently, which can make a big difference in a large house. 

Purchase price: $315,000 Cash invested: $6,000 Sale price: $375,000 This was an excellent deal, it came with 7 storage units too!