I like the idea of charging rent as well, but just a word of warning:
Charging rent will give him a whole lot of rights as a renter. Such as, you may have to give him notice to kick him, and once he is gone be responsible for his possessions etc. Look up some of the legal pitfalls of renting before going this route.
If it were me, I might have him stay as a “friend” for at least a month before charging anything. Friends have no legal rights.
If it works out, I am all for eventually charging him rent.
