A few months ago I read something about Tengu and Uchiha Madara and I looked for the theory wich is almost complete mentioned in this thread on the internet and found an interesting thread with a nice theory maybe some people even read the thread :
The Dark History of Uchiha: The Bloodline of Tengu <SPOILERS WILL GET YOU BANNED> - Naruto Forums

I hope it's not a problem to post a link to another site^^ If it is, then plz remove it or delete my whole comment