It's best if you login as root or su to root when installing these files. That way you are assured that all files are owned by user root, group root (and not owned by the userid of your non-root user) and if a package wants to set special permissions it can do so without problems due to non-root access. If you read the documentation that comes with Glibc, Gcc and other packages they recommend not to compile the packages as user root. We feel it's safe to ignore that recommendation and compile as user root anyways. Hundreds of people using LFS have done so without any problems whatsoever and we haven't encountered any bugs in the compile processes that cause harm. So it's pretty safe (never can be 100% safe though, so it's up to you what you end up doing).