In FinalBuilder there are a number of “Wait For” actions. A simple version of this would be to wait for a file on a network share. Another approach would be to wait for a process not to be running (Wait For Remote Computer). All the wait for actions have their limitations, especially when referring to network connectivity.
I suggest starting with waiting for a file to appear on a shared network drive. This way if the builds fail, or the network goes down for any reason you can add the file manually as needed. The file will then need to be remove as a pre-build step so that the shared state (file presence) is correct.