Calendar resources reference buildings; you can't delete a building if a resource calendar references it.
You'll have to list all of the resource calendars that reference the building, delete them and then delete the building.
$ gam redirect csv ./BuildingResources.csv print resources query "buildingId=test" allfields
Getting all Resource Calendars, may take some time on a large Google Workspace Account...
Got 1 Resource Calendar: Test Resource XXX - Test Resource XXX
$ more BuildingResources.csv
resourceId,resourceName,resourceEmail,resourceDescription,resourceType,buildingId,buildingName,capacity,featureInstances,floorName,floorSection,generatedResourceName,resourceCategory,userVisibleDescription
test,Test Resource XXX,c_18821kqq0bgqi...@resource.calendar.google.com,,,id:test,Test,,,,,Test-Test Resource XXX,CATEGORY_UNKNOWN,
$ gam redirect stdout ./DeleteBuildingResources.txt multiprocess redirect stderr stdout csv BuildingResources.csv gam delete resource "~resourceId"
2023-11-07T18:19:15.385-08:00,0/1,Using 1 process...
2023-11-07T18:19:15.385-08:00,0,Processing item 1/1
2023-11-07T18:19:16.474-08:00,0/1,Processing complete
$ more DeleteBuildingResources.txt
Resource Calendar: test, Deleted
$ gam delete building test
Building ID: test, Deleted
Ross