Your Windows machine and your Mac machine doesn't need to be on the same network, the Mac just needs to be accessible over the net from the Windows machine.
For the Hosted Mac Builder to work, you need to have purchased that option. Did you do that? If so you should have received a secret user id to enter into the settings there, and information on what to specify as the IP address.
And, as a sanity check, your Windows machine CAN access the open Internet, right?