No need to know anything.. the contractor will not stupidly building another story just like that..
(based on if owner say it can or cannot support).
Whether your existing stucture can take extra load or not doesn't matter.. They know how
to evaluate. They know how to reenforce the current structure and how many extra columns
are need to be added and how to make the proper foundation..
The main point is, yes, the technology to transform your house from 1 to 2 storey or 2 to 3 storey is there.
As long as you got the money.. it doesn't matter how is your existing house structure.
The worst case is, demolish existing house and rebuild from scratch

This showed that you know nuts about building or how it works. Sure hope you're not a contractor or engineer.