While installing from binary package (prepared with "quickpkg" and installed with "emerge -k") installation fails on disk space check. Can it be (disk space check) disabled somehow for this type of installation? Can it be that instead of error and installation break there is only warning? From my experience I know that ~4GB only is required to build latest versions (at least with my USE settings) thus 9GB is exaggerate for me and complicates installation.
This is already fixed in 3.4.4 and later versions. Since you didn't put version in your report i assume you use older version. Please reopen this if I am wrong in my assumptions and state what exact version you are using.