Hi,

Now it is easier to read the template, I was incorrect in what I commented on before and something I should have asked earlier was are you using Neutron Flat or Neutron VLAN/GRE? If Flat then creating new networks will fail IMHO - which is why you get this "Unable to create the network. No tenant network is available for allocation.". As it is 'Flat' there is nothing to allocate. When using GRE/VLAN there will be a range of to allocate from be it tunnels or vlans.

Example network using GRE:

Provider Network
  Network Type: gre
  Physical Network: -
   Segmentation ID: 2

For what it is worth this templates works,

It creates - a network not connected to anything (no routers)

• A subnet
• The Volume
• The server is then connected to the network created.
• The Volume is attached

I slightly edited the template to look neater, I commented out your tenantID and added the 'gateway' property for completeness.

########## Heat Template ##########
description: Generated template
heat_template_version: 2013-05-23

parameters:
    server_0_flavor:
        default: m1.tiny
        description: Flavor to use for server server_0
        type: string

    server_0_image:
        default: e35d4491-fd0d-4241-8524-8703c27608ff
        description: Image to use to boot server server_0
        type: string

resources:

    network_0:
        type: OS::Neutron::Net
        properties:
            admin_state_up: true
            name: public_net
            shared: false
            #tenant_id: 5eae73fa860c4291bab537f5e45e849b

    server_0:
        type: OS::Nova::Server
        properties:
            block_device_mapping:
            - device_name: /dev/vdb
              volume_id: { get_resource: volume_0 }
            diskConfig: AUTO
            flavor: { get_param: server_0_flavor }
            image: { get_param: server_0_image }
            name: test1
            networks: [network: { get_resource: network_0 }]

    subnet_0:
        type: OS::Neutron::Subnet
        properties:
            network_id: { get_resource: network_0 }
            cidr: 9.148.45.0/24
            dns_nameservers : [9.148.5.22]
            #gateway_ip: xx.xx.xx.xx
            allocation_pools:
            - start: 9.148.45.81
              end: 9.148.45.94

    volume_0:
        type: OS::Cinder::Volume
        properties:
            name: my_vol
            size: 1
            metadata:
                attached_mode: rw
                readonly: 'False'

I have the similar kind of issue. what is going wrong in the below yml file for creating the flat network-

It gives error- Resource Create Failed: Neutronclientexception: 503-{U'Neutronerror': {U'Message': U'Unable To Create The Network. No Tenant Network Is Available For Allocation.', U'Type': U'Nonetworkavailable', U'Detail': U''}}

heat_template_version: 2013-05-23
description: Simple template to create a flat network

resources:
  provider_01:
     type: OS::Neutron::ProviderNet
     properties:
       physical_network: physnet2
       shared: true
       network_type: flat
  network_01:
    type: OS::Neutron::Net
    properties:
       admin_state_up: true
       name: External2
       shared: true
       #admin tenant id
       tenant_id: "6ec23610836048ddb8f9294dbf89a41e"
  subnet_01:
    type: OS::Neutron::Subnet
    properties:
       name: Subnet2
       network_id: { get_resource: network_01 }
       cidr: 192.168.56.0/24
       gateway_ip: 192.168.56.1
       allocation_pools: [{"start": 192.168.56.50, "end": 192.168.56.70}]
       enable_dhcp: true
  port_01:
    type: OS::Neutron::Port
    properties:
       admin_state_up: true
       network_id: { get_resource: network_01 }
       #security_groups: "default"