Conditional Data Validation

Hey guys I have a list of items and I need someone to go through them assigning a building number, level and location to each of them. I am using drop down menus, the first choice is building and has the following options:

B1
B2
B3
B4A
B4B
B5
B7

Depending on the option selected there maybe different locations, i.e. B1 has the following available locations:

1-4
4-16
MER
ALL
KIT

Whereas B7 only has:
ALL

The third column, level, operates in a similar way.

Any ideas how to accomplish this so that I do not have to show all values?

have a read through here:

http://www.contextures.com/xlDataVal02.html

A fairly well known link when it comes to dependent lists...