pkgbuild (and pkgtool) should support BuildRequires: version, revision, and serial checking. Currently in 1.3.4, they are ignored. Attached is my fix. It is sad that svr4 depend(4) does not support this well enough to extend this idea to support Requires: similarly. I suppose someone might write a checkinstall script to do this.
pkgbuild-1.3.4 patch to fully support BuildRequires: