Well, building software on Ubuntu is fun.
I don't really know what packages etc. you need for that. I do know that Sigil is available in the Debian unstable repositories (but not yet in the current Debian release).
Give it a few years and Ubuntu might ship it too.
Arch Linux has had it since forever. And I maintain the sigil-git package for the Arch User Repository.
...
I've looked once or twice at how to package a Debian/Ubuntu package (for calibre), but couldn't really figure it out.
Maybe I could copy the version in Debian and turn it into a PPA. I hear they've got git dailybuild recipes now, and everything...