Creating SharePoint 2010 permissions levels

Following is the way to define permission level programmatically

First we need to know the permission levels available. following table contains the details:

Role	Description
EmptyMask	Has no permissions on the Web site. Not available through the user interface.
ViewListItems	View items in lists, documents in document libraries, and view Web discussion comments.
AddListItems	Add items to lists, add documents to document libraries, and add Web discussion comments.
EditListItems	Edit items in lists, edit documents in document libraries, edit Web discussion comments in documents, and customize Web Part Pages in document libraries.
DeleteListItems	Delete items from a list, documents from a document library, and Web discussion comments in documents.
ApproveItems	Approve a minor version of a list item or document.
OpenItems	View the source of documents with server-side file handlers.
ViewVersions	View past versions of a list item or document.
DeleteVersions	Delete past versions of a list item or document.
CancelCheckout	Discard or check in a document which is checked out to another user.
ManagePersonalViews	Create, change, and delete personal views of lists.
ManageLists	Create and delete lists, add or remove columns in a list, and add or remove public views of a list.
ViewFormPages	View forms, views, and application pages, and enumerate lists.
Open	Allow users to open a Web site, list, or folder to access items inside that container.
ViewPages	View pages in a Web site.
AddAndCustomizePages	Add, change, or delete HTML pages or Web Part Pages, and edit the Web site using a SharePoint Foundation–compatible editor.
ApplyThemeAndBorder	Apply a theme or borders to the entire Web site.
ApplyStyleSheets	Apply a style sheet (.css file) to the Web site.
ViewUsageData	View reports on Web site usage.
CreateSSCSite	Create a Web site using Self-Service Site Creation.
ManageSubwebs	Create subsites such as team sites, Meeting Workspace sites, and Document Workspace sites.
CreateGroups	Create a group of users that can be used anywhere within the site collection.
ManagePermissions	Create and change permission levels on the Web site and assign permissions to users and groups.
BrowseDirectories	Enumerate files and folders in a Web site using Microsoft Office SharePoint Designer 2007 and WebDAV interfaces.

And now here is the code by which we can define the custom role or permission level:


PRoleDefinition role = new SPRoleDefinition();
                role.BasePermissions = SPBasePermissions.OpenItems | SPBasePermissions.EditListItems | SPBasePermissions.ViewListItems | SPBasePermissions.ViewPages | SPBasePermissions.Open | SPBasePermissions.ViewFormPages;
                role.Name = “My Role Name”;
                role.Description = “My Role Description”;
                rootWeb.RoleDefinitions.Add(role);
Then we assign a set of permissions to an existing group in this case called MyGroup
                SPRoleAssignment roleAssignment = new SPRoleAssignment(rootWeb.SiteGroups["MyGroup"]);
                roleAssignment.RoleDefinitionBindings.Add(role);
                rootWeb.RoleAssignments.Add(roleAssignment);