Figured it out and @Charlieface was correct I was way overthinking this problem.

In my top OPENJSON call if I set this column name

`[ChildArray] nvarchar(max) '$.json_request.parentArray.childArray' as JSON`

Then I can make a simple call like this and my BuildingArea information is displayed correctly.

CROSS APPLY
OPENJSON(base.[ChildArray])
WITH (
BuildingArea int '$.Location.BuildingArea'
) AS details

Thank you @Charlieface for making me rethink my approach