MVC :: Create A Custom AuthorizeAttribute?

I have a database where i want to log my user into and for this issue i want to customize the AuthorizeAttribute i am wrong ?? have some easier way to do it ??

public class CustomAuthorizeAttribute : AuthorizeAttribute
{
// the "new" must be used here because we are overriding
// the Roles property on the underlying class
public new Authorization.SiteRoles Roles;
protected override bool AuthorizeCore(HttpContextBase httpContext)
{
if (httpContext == null)
throw new ArgumentNullException("httpContext");
string[] users = Users.Split(',');
if (!httpContext.User.Identity.IsAuthenticated)
return false;
int found = Convert.ToInt32(httpContext.Session["role"]);
return Authorization.CheckRolesCompliance(Roles);
}
}

ERROR: 'CustomAuthorizeAttribute.AuthorizeCore(System.Web.HttpContextBase)': no suitable method found to override