Once the free period is over the 100PB will cost $1 million per month in storage fees alone. Will the free month(s) even cover the retrieval and transfer fees to take 100PB out of another cloud?
To store 100PB, one can always buy 50.000 hard drives. Would only cost $2-3 million of initial payment. I wonder how much maintenance would cost to provide same availability with near storage.
Don't forget the full-time admins and hwops people. Operations costs are going to dwarf the capital investment.
Or you could leave it in the cloud where it already is and not transfer it to Google's cloud. I wasn't suggesting building your own...