If you want to point you blog hosted at blogspot.com to subdomain like http://blog.xxxx.com using Cloudflare, following are the steps:
1. Go to Basic Settings of your blog
2. Click on Third-party domain settings under Publishing
3. It will ask you to add two CNAME entries under your DNS settings. You can add as follow in Cloudflare
4. Set domain in your blog settings as http://blog.xxx.com. Save.
That's it. Sometimes it reflects immediately, sometimes it takes 24 to 48 hours as well.
Thanks!!!!!!!!!! Enjoy Programming!! :)