In Snowflake, to create a materialized view, the user must have the necessary privileges on the schema where the view will be created. These privileges are granted through roles, not directly to individual users. Therefore, the correct process is to grant the role to the user and then grant the privilege to create the materialized view to the role itself.
The statement GRANT ROLE MYROLE TO USER USER1; grants the specified role to the user, allowing them to assume that role and exercise its privileges. The subsequent statement CREATE MATERIALIZED VIEW ON SCHEMA MYDB.MYSCHEMA TO MYROLE; grants the privilege to create a materialized view within the specified schema to the role MYROLE. Any user who has been granted MYROLE can then create materialized views in MYDB.MYSCHEMA.
References:
* Snowflake Documentation on Roles
* Snowflake Documentation on Materialized Views

Data Size Limitations
The VARIANT data type imposes a 16 MB size limit on individual rows.
For some semi-structured data formats (e.g. JSON), data sets are frequently a simple concatenation of multiple documents. The JSON output from some software is composed of a single huge array containing multiple records. There is no need to separate the documents with line breaks or commas, though both are supported.
If the data exceeds 16 MB, enable the STRIP_OUTER_ARRAY file format option for the COPY INTO <table> command to remove the outer array structure and load the records into separate table rows:
copy into <table>
from @~/<file>.json
file_format = (type = 'JSON' strip_outer_array = true);
https://docs.snowflake.com/en/user-guide/semistructured-considerations.html

"The costs for sharing data with Snowflake are minimal and straightforward. Data providers simply pay Snowflake for the data they store, and data consumers pay for the compute resources their queries consume."