Building a bank

Depends on the location/underlying soil-type, but I would generally favour bricks and mortar.

Remember to include a really strong safe too.

http://www.channel4.com/programmes/bank-of-dave

i saw this start up his own bank , he called it "bank of dave"

if you email him he may be able to help

The above are a pretty fair cross-section of the sort of replies you were

bound to receive.

Good luck anyway.