To what does Bradbury compare the scene at Montag's house?
I assume you are talking about the scene at Montag's house at the beginning of Part III of the book. This is the part where the firemen have arrived at Montag's house and are going to burn it down.
If so, then the answer is that he compares it to a circus or a carnival. He talks about the tents being set up and there being a main ring where there would be various circus acts. Later on in this scene, after Montag is done burning his house down, Bradbury talks about how the circus tent has now collapsed and the show is over.