It's very difficult in this day and age to actually get an offshore bank up and running. Most jurisdictions are now actively rejecting shell banks and even if you manage to get a license/charter somewhere...getting a correspondent account will be nearly impossible. In short, other banks really wont want to deal with you. Finally, you need to have HEAPS of capital to do it.
I guess it really depends what you want to do with the bank and which sector you are targeting but the days of getting a license in a place like Vanuatu and then transacting on the interbank market/swift network are basically done.