if (User.IsInRole("rolename")) {
  // what you wan't to do.
}

GenericIdentity userIdentity = new GenericIdentity((FormsIdentity)HttpContext.Current.User.Identity.Name);

string[] roles = { "rolename1", "rolename2", "rolename3" };
GenericPrincipal userPrincipal = new GenericPrincipal(userIdentity, roles);
Context.User = userPrincipal;

if (User.IsInRole("rolename1")) {
  // what you wan't to do.
}