Generate scripts to create DB Users and their membership from existing DB

-- Create script to create the DB Users
SELECT 'CREATE USER [' + name + '] for login [' + name + ']' + char(13) + 'GO'
 from sys.database_principals
 where Type = 'S' AND default_schema_name='dbo'

-- Create script to create the Users' membership
SELECT 'EXECUTE sp_AddRoleMember ''' + roles.name + ''', ''' + users.name + '''' + char(13) + 'GO'
 from sys.database_principals users
  inner join sys.database_role_members link
   on link.member_principal_id = users.principal_id
  inner join sys.database_principals roles
   on roles.principal_id = link.role_principal_id
 WHERE users.Type = 'S' AND users.default_schema_name='dbo'

Generate scripts to create DB role and its securables from existing DB

declare @RoleName varchar(50) = 'RoleName'

-- Create script to create DB Role
select 'CREATE ROLE [' + @RoleName + ']' + char(13) + 'GO'

-- Create script to grant pemission of securable of the DB Role
select 'GRANT ' + prm.permission_name + ' ON [' + OBJECT_NAME(major_id) + '] TO [' + rol.name + ']' + char(13) COLLATE Latin1_General_CI_AS + 'GO'
from sys.database_permissions prm
    join sys.database_principals rol on
        prm.grantee_principal_id = rol.principal_id
where rol.name = @RoleName