Is it your first build? I wouldn't recommend building a bassman as your first amp. It's certainly a tricky build compared to others for a variety of reasons. First, it has 4 speakers which will be a hefty sum.
If you do a head and then a cabinet that will be even more difficult than a combo and you need general woodworking experience as well as have to know how to cover the cabinet with tolex, and that's just a few reasons. You would be better off just buying a silverface bassman and converting it.