You do not need to use a button or any macro type manipulation.
In one cell insert a list (via data validation) with all the possible buildings. Then create a dummy that will indicate #N/A if the building is not the one selected and the XY value of this building if it is the good one.
It...
To access another worksheet with data validation, you should use names.
You can create a first listbox with the name of your six lists, then create a dynamic name that select the correct list depending of the entry in the first listbox.
I think that there are a lot of very good example of...
You should use the following formula : =(A2-A1)/ABS(A1).
So if the difference between A2 and A1 is above (below) zero, the % will be greater (lower) than 0.