People often misunderstand them so you have to educate motivated sellers on what this actually entails.

So, the contractors would have to understand all the building material needed for the ADU, timing, building codes, depth of foundation, beams and brackets to use... etc. and where they would need detail would be: on the finish work: i.e. tile, window type, flooring, cabinets (type, texture, color) etc, anything that would be considered aesthetic (as one tile could be $2 per sq ft and another would be $10 dollars per sq ft) and even choosing one or the other would entail more labor work or less and hence the labor costs could change with every decision made. 

But with your son, you need to be careful that this doesn't turn into a project that can destroy your relationship.Setting the expectations in this case should entail the good, the bad, and the ugly.

If, however, you say "I want these funds to help me retire," then since that entails a much larger and longer term purpose, the potential vehicles (instruments and/or specific investments) would be different.

This mostly entails the construction of multifamily housing, hospitals, schools, etc.

Search around these forums and other resources to understand what this entails.

I'm pregnant so I can't do any heavy lifting so we'll need to hire folks to help us and it will probably entail some organizing of the garage to fit everything in there. 

I think military housing office has lists of local approved landlords, they have some involvement in the process (don't know what it entails) and the soldier's commander may get involved if they don't pay their bills.

I found one that I am interested in lending money to for his projects but do not know what all is entailed as far as securing my loan against the property and general terms/conditions.

@Jason...I understand your aversion to debt; it does entail risk.