I've written two times on a comparison between the construction industry and the software industry: Construction industry not so bad? and Software industry vs. construction industry, this will be the third time.
If you're interested in contracts, read scope limbering about "fixed price, fixed scope" contracts, by Martin Fowler. In his case in the software industry, but the same is true on the construction side. Read the following quote and you could use it for both industries:
A tripling of actuals over initial estimates isn't unusual in our industry. Mostly I believe this isn't because we are so bad at estimating (although we aren't exactly stellar at it), but it's mainly because it's so hard to get a decent set of requirements. Many delivery companies take advantage of that by low-balling the initial bid and making profit on scope changes. But this approach sours the ongoing relationship with the client - which leads to the whole industry gaining a bad reputation.
My name is Reinout van Rees and I work a lot with Python (programming language) and Django (website framework). I live in The Netherlands and I'm happily married to Annie van Rees-Kooiman.
Most of my website content is in my weblog. You can keep up to date by subscribing to the automatic feeds (for instance with Google reader):