diff --git a/build_manifest.py b/build_manifest.py
index 508555f..03cdbcd 100755
--- a/build_manifest.py
+++ b/build_manifest.py
@@ -20,6 +20,10 @@ parser.add_argument(
     dest='image_type',
     action='store',
     required=True)
+parser.add_argument(
+    '--old-manifest',
+    dest='old_manifest',
+    action='store')
 FLAGS = parser.parse_args()
 
 
@@ -28,23 +32,39 @@ class ManifestBuilder(object):
   _FILE_REGEX = '^%(image_type)s\.(?P<timestamp>\d+)\.iso$'
   _BUF_SIZE = 2 ** 16
 
-  def __init__(self, image_dir, image_type):
+  def __init__(self, image_dir, image_type, old_manifest):
     self._image_dir = image_dir
     self._file_regex = re.compile(self._FILE_REGEX % {
         'image_type': image_type,
     })
+    self._old_manifest = old_manifest
+
+  def _Rollouts(self):
+    if not self._old_manifest:
+      return {}
+    try:
+      with open(self._old_manifest, 'r') as fh:
+        parsed = json.load(fh)
+        return dict(
+            (image['timestamp'], image['rollout_‱'])
+            for image in parsed['images'])
+    except FileNotFoundError:
+      return {}
 
   def BuildManifest(self):
     ret = {
         'timestamp': int(time.time()),
         'images': [],
     }
+    rollouts = self._Rollouts()
     for filename in os.listdir(self._image_dir):
       match = self._file_regex.match(filename)
       if not match:
         continue
+      timestamp = int(match.group('timestamp'))
       image = {
-          'timestamp': match.group('timestamp'),
+          'timestamp': timestamp,
+          'rollout_‱': rollouts.get(timestamp, 0),
       }
       with open(os.path.join(self._image_dir, filename), 'rb') as fh:
         hash_obj = hashlib.sha256()
@@ -55,10 +75,11 @@ class ManifestBuilder(object):
           hash_obj.update(data)
         image['hash'] = hash_obj.hexdigest()
       ret['images'].append(image)
+    ret['images'].sort(key=lambda x: x['timestamp'], reverse=True)
     return ret
 
 
-builder = ManifestBuilder(FLAGS.image_dir, FLAGS.image_type)
+builder = ManifestBuilder(FLAGS.image_dir, FLAGS.image_type, FLAGS.old_manifest)
 manifest = builder.BuildManifest()
 json.dump(manifest, sys.stdout, indent=4)
 sys.stdout.write('\n')