A few questions about FreeBSD
Where/how should I obtain the source code (ex. through terminal, Download off website)
How (on ubuntu) should I build it?
Before I build it can I customize it (in other words is possible)?
You can check the source for FreeBSD out of version control here. The developer's handbook answers a lot of questions about developing FreeBSD. Why aren't you building it from FreeBSD itself? It seems kind of... odd to be building from Ubuntu.