Is it possible to build a chroot environment which is running FreeBSD inside of Linux, if so, how would I go about build a chroot environment from within Linux?
FreeBSD and Linux are two different kernels (well, FreeBSD users will argue with me here, but the core of FreeBSD is a different kernel), so you can’t run one on top of the other without some sort of emulation or virtualisation layer.
The easiest way to run FreeBSD on a Linux-based system is to use a virtual machine such as QEMU.
If you’re really keen, you might be able to run a pure FreeBSD chroot on a distribution with a familiar set of tools, e.g. Debian GNU/kFreeBSD. You can apparently do the opposite, i.e. run a Debian GNU/kFreeBSD chroot on top of FreeBSD. In both cases you’re using the FreeBSD kernel, there’s no Linux kernel involved.