DropDownList View Model

Question

I'm trying to produce a dropdownlist for GetAllRoles using the role provider.

I can produce the drop down in a controller using ViewData but I would like to use a View Model to produce the dropdown, but I'm unsure of the best way to create the list using a View Model?

public ActionResult GetAllRoles()
{
   ViewData["Roles"] = new SelectList(Roles.GetAllRoles());
   return View(); 
}