If you are looking to have a solid investment property that is paid with OPM and makes a little bit of cashflow that you can sell later in life for a major windfall - probably not that crazy.

Is it as simple as: "most houses in the area sell/appraise for X, figure out how to build a house for X-20%" and there's your 20% immediate equity in a new build? 

The real estate agent that "helped" me sell the property wasn't helpful or easy to deal with.

Doing this increased the value of my holding 2.5x, possibly 3x, I will know for sure when I sell in the coming year or two.With that said, DON'T DO IT.Financing, and for the most part the construction, will be the easy part  It is permitting that is the killer. 

She is looking to move to Florida, and can't sell this home due to:1) She wants top dollar2) The home sits next to a transfer pump station (eyesore)3) It sits on a main road (traffic, noise)4) The community pool is behind the home and visible from the deckThe home is in immaculate condition.

If you’re going this route, make sure the PM company is under the same roof, the rehabs are quality and they aren’t selling to you above market (appraisal price).

Somethings that newer investors don't think about but should be addressed int the OA is what happens to the upon death - who gets the company, is there portion bought out by the other owners, at what price, what happens when one owner wants to sell, etc.

Of course they all have personal guarantee.I am referring to rules Freddie has here https://guide.freddiemac.com/app/guide/section/5401.2 or Fannie has here https://selling-guide.fanniemae.com/sel/b3-6-05/monthly-debt... that debt paid for 12 months or longer by business can be excluded.

I've heard about turnkey companies (properties that a company owns, is already rented, and ready to sell with tenants in it) but am not familiar with any names of companies.

For my investors, even with my GC markup, they still spend about 80% ARV from doing things normally so even they won't make much money if they sell it right away, but there's some equity in it for them and the cost is lower than buying.