i'm after detailed information on Construction Cost Overruns, i'm
looking for literature on this topic, I don't want case studies or
examples of it, just information on what Construction Cost Overruns
are and how to prevent etc. i would like an answer of approx 1500
words

what i'm after is as follows:

What are Construction Cost Overruns?
How to avoid/reduce/prevent Construction Cost Overruns
detailed reasons why Construction Cost Overruns occur etc.

When you have a contractor build or repair something for you, it is
customary for the contractor to give you an estimate of the total
cost. If the cost is less than expected the contractor makes a large
profit. If it is more the contractor asks for more money = cost over
run. In some states you can refuse to pay more than a small additional
amout (under some conditions)

This article may be helpful:

http://www.thespaceplace.net/articles/wells200209.htm