For the block see Banker's Chest
To build a Bank you have to make a Build Sign, with bank1 in the second line.
To view the floorplan for this building, go to your .minecraft folder, then into the resources folder, and finally to the floorplan folder.
There are 2 stages for this building.
- bank1 dimensions are: 11 wide x 11 long x 7 high.
- bank2 dimensions are: 11 wide x 11 long x 9 high.
The chest should be placed on the 6th block from the right, and the 6th block from the forward edge.