Is it possible to host a central model on the cloud so that people from different offices can work on the same project?
Yes... I suppose you could...
You'd sure want to make sure everyone has a VERY VERY fast uplink/downlink connection. (We're talking 50Mbps+).
A better idea is to deploy Revit server through your WAN and inter-office.
The ghetto-I-would-not-try-this solutions would be to either:
A: Put the central model on someone's computer's "dropbox"... but that's kind of dangerous.
B: Put the central model on an FTP server. Map a network drive to be the FTP server address.
Please read this help article: