diff --git a/ocfl/inventory.py b/ocfl/inventory.py
index 240d370..3745210 100644
--- a/ocfl/inventory.py
+++ b/ocfl/inventory.py
@@ -83,13 +83,13 @@ def digest_algorithm(self, value):
         self.data["digestAlgorithm"] = value
 
     @property
-    def identifier(self):
-        """Get object identifier."""
+    def id(self):
+        """Get object id."""
         return self.data.get("id")
 
-    @identifier.setter
-    def identifier(self, value):
-        """Set object identifier."""
+    @id.setter
+    def id(self, value):
+        """Set object id."""
         self.data["id"] = value
 
     @property
@@ -126,6 +126,11 @@ def manifest(self):
         """
         return self.data.get("manifest", {})
 
+    @manifest.setter
+    def manifest(self, value):
+        """Set the manifest to the supplied dict()."""
+        self.data["manifest"] = value
+
     @property
     def manifest_add_if_not_present(self):
         """Get the manifest of digests and corresponding content paths.
@@ -138,6 +143,16 @@ def manifest_add_if_not_present(self):
             self.data["manifest"] = {}
         return self.data["manifest"]
 
+    @property
+    def fixity(self):
+        """Get fixity block as dict()."""
+        return self.data["fixity"]
+
+    @fixity.setter
+    def fixity(self, value):
+        """Set the fixity to the supplied dict()."""
+        self.data["fixity"] = value
+
     @property
     def content(self):
         """Get all the content paths and their digests stored within the object.
@@ -172,6 +187,11 @@ def versions_block(self):
         """
         return self.data.get("versions", {})
 
+    @versions_block.setter
+    def versions_block(self, value):
+        """Set dict of the versions block."""
+        self.data["versions"] = value
+
     @property
     def version_directories(self):
         """List of all version directories.
@@ -291,6 +311,24 @@ def as_json(self):
         """Serlialize JSON representation."""
         return json.dumps(self.data, sort_keys=True, indent=2)
 
+    def init_manifest_and_versions(self):
+        """Initialize manifest and versions blocks for building new inventory."""
+        self.manifest = {}
+        self.versions_block = {}
+
+    def add_fixity_type(self, digest_algorithm):
+        """Add fixity type with no file data.
+
+        Arguments:
+            digest_algorithm: string of the digest algorithm specifying this
+                fixity type
+
+        If there is no fixity data then will start a fixity block.
+        """
+        if "fixity" not in self.data:
+            self.data["fixity"] = {}
+        self.data["fixity"][digest_algorithm] = {}
+
 
 class Version():
     """Version class to represent version information in an Inventory.
diff --git a/ocfl/object.py b/ocfl/object.py
index 88e2d92..fcd95e7 100755
--- a/ocfl/object.py
+++ b/ocfl/object.py
@@ -22,6 +22,7 @@
 import fs.copy
 
 from .digest import file_digest, normalized_digest
+from .inventory import Inventory
 from .inventory_validator import InventoryValidator
 from .object_utils import make_unused_filepath, next_version, \
     parse_version_directory, ObjectException
@@ -170,25 +171,23 @@ def map_filepath(self, filepath, vdir, used):
     def start_inventory(self):
         """Create inventory start with metadata from self.
 
-        Returns the start of an inventory dict based on the instance data
+        Returns the start of an Inventory object based on the instance data
         in this object.
         """
-        inventory = dict({
-            'id': self.id,
-            'type': 'https://ocfl.io/' + self.spec_version + '/spec/#inventory',
-            'digestAlgorithm': self.digest_algorithm,
-            'versions': {},
-            'manifest': {}
-        })
+        inventory = Inventory()
+        inventory.id = self.id
+        inventory.spec_version = self.spec_version
+        inventory.digest_algorithm = self.digest_algorithm
+        inventory.init_manifest_and_versions()
         # Add contentDirectory if not 'content'
         if self.content_directory != 'content':
-            inventory['contentDirectory'] = self.content_directory
+            inventory.content_directory = self.content_directory
         # Add fixity section if requested
         if self.fixity is not None and len(self.fixity) > 0:
-            inventory['fixity'] = {}
             for fixity_type in self.fixity:
-                inventory['fixity'][fixity_type] = {}
+                inventory.add_fixity_type(fixity_type)
         else:
+            # Make sure None rather than just zero length
             self.fixity = None
         return inventory
 
@@ -275,7 +274,7 @@ def build_inventory(self, src_fs, versions_metadata=None):
         """
         if versions_metadata is None:
             versions_metadata = {}
-        inventory = self.start_inventory()
+        inventory = self.start_inventory().data
         # Find the versions
         versions = {}
         for vdir in src_fs.listdir('/'):
@@ -398,23 +397,22 @@ def create(self, srcdir, metadata=None, objdir=None):
             self.open_fs(objdir, create=True)
         inventory = self.start_inventory()
         vdir = 'v1'
-        manifest_to_srcfile = self.add_version(inventory=inventory, src_fs=src_fs,
+        manifest_to_srcfile = self.add_version(inventory=inventory.data, src_fs=src_fs,
                                                src_dir='', vdir=vdir,
                                                metadata=metadata)
         if objdir is None:
-            return inventory
-        # Else write out object
-        self.write_inventory_and_sidecar(inventory, vdir)
-        # Write object declaration, inventory and sidecar
+            return inventory.data
+        # Write out v1 object
+        self.write_inventory_and_sidecar(inventory.data, vdir)
+        # Write object root with object declaration, inventory and sidecar
         self.write_object_declaration()
-        self.write_inventory_and_sidecar(inventory)
+        self.write_inventory_and_sidecar(inventory.data)
         # Write version files
-        for paths in inventory['manifest'].values():
-            for path in paths:
-                srcfile = manifest_to_srcfile[path]
-                self.copy_into_object(src_fs, srcfile, path, create_dirs=True)
+        for path in inventory.content_paths:
+            srcfile = manifest_to_srcfile[path]
+            self.copy_into_object(src_fs, srcfile, path, create_dirs=True)
         logging.info("Created OCFL object %s in %s", self.id, objdir)
-        return inventory
+        return inventory.data
 
     def update(self, objdir, srcdir=None, metadata=None):
         """Update object creating a new version with content matching srcdir.
diff --git a/tests/test_inventory.py b/tests/test_inventory.py
index 58da822..bf6ff41 100644
--- a/tests/test_inventory.py
+++ b/tests/test_inventory.py
@@ -16,7 +16,7 @@ def test_getter_properties_minimal_example(self):
         inv = Inventory(filepath="fixtures/1.1/good-objects/minimal_one_version_one_file/inventory.json")
         self.assertEqual(inv.spec_version, "1.1")
         self.assertEqual(inv.digest_algorithm, "sha512")
-        self.assertEqual(inv.identifier, "ark:123/abc")
+        self.assertEqual(inv.id, "ark:123/abc")
         self.assertEqual(inv.head, "v1")
         self.assertEqual(inv.content_paths, ["v1/content/a_file.txt"])
         self.assertEqual(inv.digest_for_content_path("v1/content/a_file.txt"),
@@ -42,7 +42,7 @@ def test_creation_of_minimal_example(self):
         inv = Inventory()
         inv.spec_version = "1.1"
         inv.digest_algorithm = "sha512"
-        inv.identifier = "ark:123/abc"
+        inv.id = "ark:123/abc"
         v = inv.add_version()
         v.created = "2019-01-01T02:03:04Z"
         v.message = "An version with one file"
diff --git a/tests/test_object.py b/tests/test_object.py
index 94a2973..e494a5f 100644
--- a/tests/test_object.py
+++ b/tests/test_object.py
@@ -47,22 +47,23 @@ def test04_start_inventory(self):
         """Test start_inventory mehthod stub."""
         oo = Object(identifier="info:a", digest_algorithm="sha256")
         inventory = oo.start_inventory()
-        self.assertEqual(inventory['id'], "info:a")
-        self.assertEqual(inventory['digestAlgorithm'], "sha256")
-        self.assertEqual(inventory['versions'], {})
-        self.assertEqual(inventory['manifest'], {})
-        self.assertNotIn('contentDirectory', inventory)
-        self.assertNotIn('fixity', inventory)
+        self.assertEqual(inventory.id, "info:a")
+        self.assertEqual(inventory.digest_algorithm, "sha256")
+        self.assertEqual(inventory.versions_block, {})
+        self.assertEqual(inventory.manifest, {})
+        self.assertNotIn('contentDirectory', inventory.data)
+        self.assertNotIn('fixity', inventory.data)
+        #
         oo = Object(identifier="info:b", digest_algorithm="sha256",
                     fixity=['md5', 'sha1'])
         inventory = oo.start_inventory()
-        self.assertEqual(inventory['fixity'], {'md5': {}, 'sha1': {}})
+        self.assertEqual(inventory.fixity, {'md5': {}, 'sha1': {}})
         #
         oo = Object(identifier="info:b", content_directory="stuff")
         inventory = oo.start_inventory()
-        self.assertEqual(inventory['id'], "info:b")
-        self.assertEqual(inventory['contentDirectory'], "stuff")
-        self.assertEqual(inventory['digestAlgorithm'], "sha512")
+        self.assertEqual(inventory.id, "info:b")
+        self.assertEqual(inventory.content_directory, "stuff")
+        self.assertEqual(inventory.digest_algorithm, "sha512")
 
     def test05_add_version(self):
         """Test add_version method."""