I'm not sure about your objective.
An SQLite DB is a single file.
Open the SQLite DB and "write" to it.

It is possible to dynamically expand and contract the memory usage of an SQlite DB. That can be a good technique for memory intensive operation like indexing a DB. I have applications that jump the memory from 20 MB (default) to 200 MB of memory.

In general, I would not recommend trying to force SQLite to generate a DB entirely within memory.

In general, open the new DB and let the program do it.