I am the sagemath PPA maintainer.
The PPA (and even the binary tarballs downloaded from sagemath) is not really intended for adding optional packages but it is possible.
It is dangerous to build everything as root, as you found from the sage error!
Changing the ownership may essentially break apt, or on a multi-user system be insecure for your user.
You need sagemath-upstream-binary-full, which does include the src and build and git folders if you really want to do this.
If you regularly use optional packages, it is preferred to install from source, (fix permissions on a multi-user system to a new user like sagemath or root), sage -i your packages (fix permissions after), and join the low-traffic sage-release mailing list which will announce new releases, and use sage -upgrade which will only download and compile parts that changed.
It is generally not a good idea to install Sage as a root user.
I don't believe that Sage is installed as root. I've updated with the error obtained by trying to install topcom without sudo.
Well, /usr/lib certainly does not look like being inside your home dir...
Maybe it is a Sage installation through some distro package manager... (?)
How did you install Sage on your computer ? Did you use the PPA ? Did you download the binaries ? id you compile it yourself ?