how to build a foundation for a new room in fresno ca?

Answer 1

Lets start with slab on grade.....
Obtain all necessary permits.
Drive pilings as per your engineers requirements.
Form for concrete as per your engineers requirements.
Install re-bar as per your engineers requirements.
Pour Foundation using concrete formulated to your engineers requirements.

Pier Construction goes pretty much the same way, but more carpentry.
The gist of the matter is that you need a qualified engineer to design this foundation. Perhaps a local builder could manage this as well. Construction techniques differ vastly with regional needs.