The Adjutant project is building workflows for project (i.e. tenant) management (amongst other things). That is probably the best place to implement what you're trying to do. (It is an official OpenStack project.)

The other option is to trigger something off of events. To do this as a regular user, you could trigger off an event alarm and use a Zaqar subscription to execute a Mistral workflow that creates the network environment (example in another context). However, IIUC you are speaking as a cloud operator and therefore have no need to restrict yourself to APIs a regular user can access. So you could write something to listen to oslo.notification events directly and make the API calls you want.