Advice Needed: Helping my mother build homes

[Cian O'Donnell]

Hi Everyone, I am helping my mother evaluate an opportunity to build 3 houses on her land as a nest egg for retirement. She means everything to me and I would really like to thoughtfully evaluate this opportunity for her.

I have used a calculator here (Link should include calculations) and would like to know of any glaringly obvious errors/omissions? I would appreciate an experienced set of eyes to review with and ask a couple of questions to, either by email or even virtual meeting, if comfortable. 

Thanks in advance to this great community!