If you want 100TB, you need a bigger NAS than most, and that makes most of the DIY NAS not so good. 2-4 drives seems to be where DIY shines. These days motherboards often stop at 4x sata, so you'll need a HBA or USB (eww).

Personally, I just don't have that much data, 24TB mirrored for important data is probably enough, and I have my old mirror set avaialable for media like recorded tv and maybe dvds and blu-rays if I can figure out a way to play them that I like better than just putting the discs in the machine.