[pacman-dev] Disk Space

I'm a little new to package management coding, so forgive my stupid question, but I'm wondering if there is a way to get the current package size. For example, like Aarons example, if foobar-1.0 is installed, and we got the size of foobar then we should have a reasonable size estimate of foobar-1.1. If we took that estimate, multiply by 10% and compare that number to the disk space remaining, would that catch 99% of the errors? If there isn't a current mechanism we could have a function that adds the total size of all the installed apps files and return that to the upgrade function. What about that coupled with a prompt if disk space seems low, say below 100-200 mb? I'd be willing to help with whatever patches are necessary for this.