McNeill 1992, pp. 39–40
The cost of building a castle varied according to factors such as their complexity and transport costs for material. for lords of smaller areas, castle building was a very serious and costly undertaking. It was usual for a stone castle to take the best part of a decade to finish. The cost of a large castle built over this time (anywhere from £1,000 to £10,000) would take the income from several manors, severely impacting a lord's finances.
McNeill 1992, pp. 39–40
Not only were stone castles expensive to build in the first place, but their maintenance was a constant drain. They contained a lot of timber, which was often unseasoned and as a result needed careful upkeep. 
The positioning of castles was influenced by the available terrain. Whereas hill castles such as Marksburg were common in Germany, where 66 per cent of all known medieval were highland area while 34 per cent were on low-lying land, they formed a minority of sites in England. Because of the range of functions they had to fulfil, castles were built in a variety of locations. Multiple factors were considered when choosing a site, balancing between the need for a defendable position with other considerations such as proximity to resources. For instance many castles are located near Roman roads, which remained important transport routes in the Middle Ages, or could lead to the alteration or creation of new road systems in the area. Where available it was common to exploit pre-existing defences such as building with a Roman fort or the ramparts of an Iron Age hillfort. A prominent site that overlooked the surrounding area and offered some natural defences may also have been chosen because its visibility made it a symbol of power. Urban castles were particularly important in controlling centres of population and production, especially with an invading force, for instance in the aftermath of the Norman Conquest of England in the 11th century the majority of royal castles were built in or near towns. 
As castles were not simply military buildings but centres of administration and symbols of power, they had a significant impact on the surrounding landscape. Rural castles were often associated with mills and field systems due to their role in managing the lord's estate,which gave them greater influence over resources. Others were adjacent to or in royal forests or deer parks and were important in their upkeep. Fish ponds were a luxury of the lordly elite, and many were found next to castles. Not only were they practical in that they ensured a water supply and fresh fish, but they were a status symbol as they were expensive to build and maintain.
Medieval Castles were huge protection camps made to protect the king. They had every kind of defense known to medieval man. From murder holes, to arrow-loops, a castle had it.
Medieval castles were usually built on a high rocky cliff located by water. Castle locations were very hard to find and sometimes months were spent looking for one. A moat was built around the castle and was usually filled with sewage and bathroom
“goodies.” All these things played an important part in keeping the castle strong and ready to fight.
A couple other defenses the castle had were murder holes; soldiers would dump many things on the sieging warriors. Another tactic was the arrow-loops; a small slender cut in the castle wall that arrows could be shot out from but not…