Req for some help in figuring out table create grants

Hi

I am new to postgres and I am lost in figuring out how the privilege grants are dealt with.

I have a two roles my_connect role has

GRANT CONNECT ON DATABASE mydb TO my_connect;

And my_developer with the following grants:

GRANT SELECT ON ALL TABLES IN SCHEMA PUBLIC TO my_developer;
GRANT SELECT ON ALL SEQUENCES IN SCHEMA PUBLIC TO my_developer;
GRANT EXECUTE ON ALL FUNCTIONS IN SCHEMA PUBLIC TO my_developer;

Now when I create a user with no privs and grant only these roles with inherit, what does allow the user to create a table in the public schema? Shouldn't these privs limit the table creation for the user?

If I want to limit the user's ability of operation to the role, that were granted, how do I accomplish that?

Any help will be much appreciated. Thanks for all your responses in advance.

Thanx,
Sam