I have always wondered what went into choosing a location for a castle. I figure that defensive locations were favored, but were local resources and population also major factors? Did castles often spring up around a village or did the walls come then the village/population? How long on average did it take for the walls to be completed and during that time was there a standing army to protect the construction?
Edit: I am mainly interested in castles during the middle ages in Europe.
This is very broad question, too broad - the middle ages is approximately 1000 years of history across many political and social worlds. Castles in that time changed fantastically and range from transient wood forts to massive stone edifices encompassing hamlets and villages. I have been living these last 2 months in a 13th century castle in southern France, the tower of which provides me a view of four more castles built within 20 years of each other, each different in construction and origin. I could give you correct yet contradictory answers for every one of your questions.
The history of the middle ages is interesting because of the particular stories that arise, and not because of generic mythology of the distant past. So, I recommend you specify precise castles that interest you to discuss, because there isn't a 'typical castle' of the middle ages. If someone does give you a response of a typical castle, it will be generic as to be meaningless, or it will be an example that could be contradicted.