I’ve seen new construction properties in AAA+ areas get trashed at mind boggling levels.

If thats the case you could get a line of credit secured by your land that will get paid off when you close on the construction loan.

Need a referral for reliable trustworthy contractor/construction crew in the  Dallas and Oklahoma areas?

Traditional mortgages aren't for construction sites.

As someone who used to work in my dad's construction business in NY I can tell you that when you have three layers of roofing and a foot an half of snow sitting for weeks on a roof on an older house, weight can become a big problem. 

The idea is to consider the single-wide as the "primary" unit (that's how it's being sold) and apply for a construction loan to finance both the primary unit (the man home) and the future ADU. 

New homes are sold before the construction is even finished. 

I know Richmond has tons of little pockets and it seems like there’s always new construction

For example, I did not check as many references as I should have for the contractor, I did not know a lot about his construction background or past successful projects.

Their husband works in sales in the construction industry so well connected to the builders in the region.