Boo Radley's house has several features that could be considered symbolic or representative of something else.
First, Boo's house is described in shades of gray. The house used to be white, but with time and age, the color has faded. Gray can often represent confusion, which fits in the case of Boo Radley. The kids have no idea who he really is until the end of the book. Furthermore, the color gray can represent a fall from white. White represents purity and innocence. In the eyes of the community and in the eyes of Boo's own father, Boo failed to do what was right. He has forever been in the shadow of the community as a result of his adventures as a teenager.
Boo is considered a ghost in many ways. The house of a ghost is considered haunted, and the children treat the Radley home as such. This house is where the kids find much trouble: the dog dies right there, Jem loses his pants, Radley pecans can kill you, and Scout falls out of the tire in the front yard there.
However, it is also the place where the tree with the knothole provides children with gifts from an unknown giver. Scout receives a blanket from an unknown care-taker during the night of Maudie's fire. Finally, it is in the shadows near this that Jem is rescued by an unknown hero, who is later revealed to be Boo Radley.
This house represents many ideas: confusion, ghosts, the unknown, and a hero in disguise. It also helps develop the theme that things aren't always what they seem.