In order to bungle a bungalow, the first obvious step is to find a bungalow. Finding one that has some historic significance increases your "bungling factor". Finding one that fits very nicely in a neighborhood of like bungalows increases you bungling factor even more!
Now that you have your bungalow, it is time to get started.
Step one: remove the roof.
Keeping the home open to the elements so that it might maximize the rain and moisture infiltration is also key.