There are already many standard build specification formats: CMake, autotools, Meson. For each, most distro's package managers can build the software with very little configuration, e.g. Debian's debhelper will cover most standard build systems and Gentoo has eclasses that you just need to inherit in a package. I'm not sure that adding another makes things easier.

Configuration options will need to be specified manually if you want any but I don't see a way around that as they are both package-specific and also something where distros want to differ.

For dependencies there are usually language-specific registries and pkg-config for C/C++-land. Some distros (e.g. RPM-based-ones) already support specifying dependencies by the pkg-config names or library SONAMEs. There is no distro-agnostic way to specfy your dependencies except for a README as far as I know - this would be something worth specifying.

You'll invent new standard and have N+1 standards.

It's not as if package formats can't be declarative - just that some issue always turns up in package X or Y that the declarative format didn't anticipate.

I think there may indeed be tools to convert these formats but in the end the devils are always in some distro-specific set of details that make life miserable. e.g. your library has some option enabled or doesn't and some other package in that distro needs it and so on and on.

Congrats you just invented containers :P