PHP to show block only if page does not exist?

I am creating a social network and want to show a block to create a user profile page only if that page does not exist. Also, there would be a variable in the page's name as it would be something like: content/username-1 (so the username would be different for each user)

I am wondering if anyone can help with the PHP condition that I would put on a block to show only if a page does not exist yet for the current user...

Another way to do this would be something like checking if any page has been created by current user for specific node type and showing block only when no pages of node type have been created by currently logged in user (as they will only create 1 page of that node type)

Thanks for any help on this as I'm kind of stuck on this part.