I have gone through that process and I tell you it's normal. Your site wilk be back after few hours. Maybe 1-2 hours.
I have my ssl from namecheap shared hosting. Then I connect my site with Cloudflare.
When you connect your Cloudflare, your site will be un-available for a few hours. It has something to do with dns population whatsoever.
Don't install any ssl plugin. You must contact your hosting provider to do the installation of ssl.
After your site is working with ssl, then connect your site to Cloudflare.