Hi, Welcome to OpenStreetMap.

A building on the ground surface would, (by OSM), be designated as layer=0. Layer=0 is the case for most buildings, thus for OSM, in the absence of a layer tag, layer=0 is implied. Thus no layer tag is needed here.

It's OSM practice when something like the bank ceases to trade the relevant tags are appended with disused. Then other folk know exactly what has  happened and other mappers won't add the details back. I've added the tags disused:amenity=bank
disused:name=Barclays Bank.

Regards Bernard.