Libero changes your type before the move so it would cause the Pokémon to be a Normal Type. Example. Before Cinderace uses Roost, it turns into a Normal Type. Since Cinderace is now pure Flying, Roost causes Cinderace to be a Normal Type. It would be the same with Protean.
Source: The pages on these abilities and Roost and a little bit of knowledge. Hope this helps!