C# Code to create a new permission level and add a user to the a list with that permission level.

Here is the code to  create a new permission level and add a user to  the list " UserList" 

using System;
using Microsoft.SharePoint.Client;

namespace NewRole
{
    class RoleDefinitionExample
    {
        static void Main()
        {
            string siteUrl = "http://MyServer/sites/MySiteCollection";

            ClientContext clientContext = new ClientContext(siteUrl);
            Site collSite = clientContext.Site;
            Web site = clientContext.Web;

            // Set up permissions.
            BasePermissions permissions = new BasePermissions();
            permissions.Set(PermissionKind.ViewListItems);
            permissions.Set(PermissionKind.AddListItems);
            permissions.Set(PermissionKind.EditListItems);
            permissions.Set(PermissionKind.DeleteListItems);

            // Create a new role definition.
            RoleDefinitionCreationInformation rdcInfo = new RoleDefinitionCreationInformation();
            rdcInfo.Name = "Manage List Items";
            rdcInfo.Description = "Allows a user to manage list items";
            rdcInfo.BasePermissions = permissions;
            RoleDefinition roleDef = collSite.RootWeb.RoleDefinitions.Add(rdcInfo);

            // Create a new RoleDefinitionBindingCollection object.
            RoleDefinitionBindingCollection collRDB = new RoleDefinitionBindingCollection(clientContext);
            // Add the role to the collection.
            collRDB.Add(roleDef);

            // Get the list to work with and break permissions so its permissions can be managed directly.
            List targetList = site.Lists.GetByTitle("UserList");
            targetList.BreakRoleInheritance(true, false);

            // Get the RoleAssignmentCollection for the target list.
            RoleAssignmentCollection collRoleAssign = targetList.RoleAssignments;
            // Add the user to the target list and assign the user to the new RoleDefinitionBindingCollection.
            RoleAssignment rollAssign = collRoleAssign.Add(site.CurrentUser, collRDB);

            clientContext.ExecuteQuery();

            Console.WriteLine("Security modified");
        }
    }
}