I would start by contacting the housing authority in the county were your rentals are - or do a google search. 

Through SEO optimization, you can make sure that your website shows on Google's first page or higher on your search results. 

I've talked to a few contractors from google search with disappointing results.

You can google and find products ranked by reliability.

There are a ton of empty lots across Detroit, which seem in theory like "easy" places to pop up a pre-fab SFH or small multi.I did some preliminary research here and via Google and see that most people's experiences seem pretty positive with key draws being the cost = less than or equal to standard construction, materials being eco-friendly and sturdy, shorter construction time, similar appraisal value, to name a few.My questions:Can anyone share any experiences specific to Detroit or the surrounding area with regards to permitting or legal pitfalls to avoid or hurdles to jump over?

If you are unsure, then you can Google that to determine if you meet the criteria.  

I've read several Google search references that give contradicting advice. 

Search Google and see if you can find one in your market or your investment market that will take a consultation call over the phone.

I've never used a national company, but you can just google (state) + registered agent and you'll get a bunch of results for what you're looking for.

Do that then cross reference with a solid Google search, and you should be ready to go!