AD 'Building' and 'Department' info is not currently scanned by Lansweeper, 'Location' info is. For an overview of AD fields scanned by Lansweeper, please have a look at tblADComputers and tblADusers within the Lansweeper report builder. The report builder can be found in the Lansweeper configuration console under Reports & Alerts\Report Builder.
You can use the script below to insert values from tblADComputers.Location into tblCompCustom.Location (location custom field) as well. Copy and paste the script into the Lansweeper configuration console under Lansweeper\Database Scripts and hit the "Execute sql script" button.
UPDATE tblCompCustom
SET Location = tblADComputers.Location
FROM tblCompCustom INNER JOIN
tblADComputers ON tblCompCustom.Computername = tblADComputers.Computername