First of all of if you leave the BTC on Coinbase then you will not get BCC. Here is the official news by Coinbase-
"
...In the event of two separate blockchains after August 1, 2017 we will only support one version. We have no plans to support the Bitcoin Cash fork. We have made this decision because it is hard to predict how long the alternative version of bitcoin will survive and if Bitcoin Cash will have future market value."....
https://blog.coinbase.com/update-for-customers-with-bitcoin-stored-on-coinbase-99e2d4790a53So its clear that you need to move your BTC somewhere else. One solution can be to cold storage, if yes then use bitaddress and generate private keys. You can search how to make paper wallet in forum or google. If you don't want to enter into such complications, you can alternatively send BTC to some exchanges which supporting BCC. Some names- Cryptopay, FreeBitco.in, etc. But keep in mind you will receive BCC after few days in this case and you could miss high prices to sell BCC.