The room under the roof? You mean the attic? The example is true – it is a room that often needs to be protected against heat loss. But the word is not ‘isolated’, it is ‘insulated.’
You insulate your roof, meaning you put some special insulation padding in it, to stop the heat escaping.
Isolate means something completely different. It means to remove something far from everything else. If someone has a contagious disease, for example, you try and isolate them, so the rest of the people don’t catch it. Or if a prisoner misbehaves, or poses a threat to other prisoners, the guards might isolate him, meaning put him in a cell on his own.