The B&B Thalas is not far from the metro station Cornelia (line A).
As you get to the Cornelia station, take the exit to Via Boccea, then walk towards Via Pineta Sacchetti (the pinewood), behind the big bus station. On your right you'll find a street named Via Nostra Signora di Lourdes (there's a pizzeria at the corner).
Enter this street until the traffic light and on your left you'll find Via Patetta. Proceed to the number 49.