How to create or copy permission levels programmatically

The class representing the permission level in SharePoint is the SPRoleDefinition one: http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.sproledefinition.aspx
To modifies the permissions, you have to use the BasePermissions property (SPBasePermissions enumeration): http://msdn.microsoft.com/en-us/library/microsoft.sharepoint.sproledefinition.basepermissions.aspx

Hereunder is the Permission Levels page of a SharePoint site before:



The following piece of code shows how to create a new permission level:

using (SPSite siteCollection = new SPSite("http://myserver:38000/sites/Test"))

{

    using (SPWeb site = siteCollection.OpenWeb(siteCollection.RootWeb.ID))

    {

        try

        {

            site.AllowUnsafeUpdates = true;

            // This code adds a new permission level

            SPRoleDefinition newRoleDefinitionTest = new SPRoleDefinition();

            newRoleDefinitionTest.BasePermissions = SPBasePermissions.ViewListItems | SPBasePermissions.OpenItems | SPBasePermissions.EditListItems | SPBasePermissions.AddListItems | SPBasePermissions.ViewVersions;

            newRoleDefinitionTest.Name = "Test";

            newRoleDefinitionTest.Description = "This is a permission level created for testing.";

            site.RoleDefinitions.Add(newRoleDefinitionTest);

            site.Update();

        }

        catch(Exception ex)

        {

            Console.WriteLine(ex.Message);

        }

        finally

        {

            site.AllowUnsafeUpdates = false;

        }

    }

}

The following piece of code shows how to copy a permission level (in this case the permission level of the Reader role) and to add two new permissions to it:

using (SPSite siteCollection = new SPSite("http://myserver:38000/sites/Test"))

{

    using (SPWeb site = siteCollection.OpenWeb(siteCollection.RootWeb.ID))

    {

        try

        {

            site.AllowUnsafeUpdates = true;

            // This code copies the Read permission level (Reader role) and adds AddListItems and EditListItems permissions

            SPRoleDefinition roleDefinitionRead = site.RoleDefinitions.GetByType(SPRoleType.Reader);

            SPRoleDefinition newRoleDefinitionAdvancedRead = new SPRoleDefinition(roleDefinitionRead);

            newRoleDefinitionAdvancedRead.BasePermissions |= SPBasePermissions.AddListItems | SPBasePermissions.EditListItems;

            newRoleDefinitionAdvancedRead.Name = "Advanced Read";

            newRoleDefinitionAdvancedRead.Description = "This the Read permission level + AddListItems + EditListItems";

            site.RoleDefinitions.Add(newRoleDefinitionAdvancedRead);

            site.Update();

        }

        catch(Exception ex)

        {

            Console.WriteLine(ex.Message);

        }

        finally

        {

            site.AllowUnsafeUpdates = false;

        }

    }

}

Hereunder are the Permission Levels page and the Edit Permission Level pages after: