How to convert a D7 db_query object to string?
I can't see any benefit to doing that, are you sure you're not trying to get the OFFICE_ID value like this?:

$office_ids = db_query('SELECT OFFICE_ID FROM sage.OFFICE');
foreach($office_ids as $office) {
  ...
  // Depending on your database settings this might actually be lower case, i.e. $office-&gt;office_id
  $path = 'office-' . $office-&gt;OFFICE_ID;
}