Estimating construction projects is much easier than software.
Roads? In any developed country, they are a known quantity. Their cost and time can probably be estimated to with a small delta, calculated by the foot (or metre). I think every single street in my city is pretty built the same way.
Buildings? Ask a developer in a new subdivision how long House Model B will take to put up after they've already built 5 of 'em. A new office tower? We've built a few of those.
Bridges? Choose one of the three designs. It's not like you're going to bother trying to invent a new kind.
Your particular piece of software? Unfortunately, still much more like a unique little masterpiece than a construction project, and much more difficult to forecast.
And yet construction projects are notorious for going over budget... for small off-the-shelf construction projects (2 miles of road for example) it's feasible, but a new motorway?
And if the weather's bad, the contractor will be claiming for more down days in that 2 miles of road than expected - so there is still an expensive variable.
Off the top of my head, two reasons construction projects are notorious for going over budget would be because of labour (union) costs, not to mention corruption (cf. Quebec's Charbonneau Commission).
Why single out weather? Lots of human activities are impacted by weather. What's the analogy to software?
> Why single out weather? Lots of human activities are impacted by weather. What's the analogy to software?
To point out there's still a large variable in the construction projects isted, and it's not as cut and dried as you made out.
Here in the UK (land of rain) the weather is a major source of extra costs in small (under £1M) projects. Source: chief surveyor of a county council's highway department.
The contracts are well negotiated by the construction firm (and I understand is an industry standard clause, so you can't just hire a different firm), so if work can't be done on your project due to inclement weather, they will put in a claime for their labour costs for thse days, plus hire of plant that's on-site. AFAIK they won't get the full cost, but they're good at putting in frequent claims :)
Roads? In any developed country, they are a known quantity. Their cost and time can probably be estimated to with a small delta, calculated by the foot (or metre). I think every single street in my city is pretty built the same way.
Buildings? Ask a developer in a new subdivision how long House Model B will take to put up after they've already built 5 of 'em. A new office tower? We've built a few of those.
Bridges? Choose one of the three designs. It's not like you're going to bother trying to invent a new kind.
Your particular piece of software? Unfortunately, still much more like a unique little masterpiece than a construction project, and much more difficult to forecast.