I mean, it's possible for locations at other levels because I can override the canCreate method of that specific container page type.
But if directly under Site Content. There is no way for me to restrict user creating pages there. If a user can create a certain page type, then he can create as many instances as he wants along with the Home page and the 404 page.
Is there anyway I can solve this?

Thanks :>

Try this code in pages.php, it allows page creation under Site Content only for Administrators...

public function onBeforeWrite() {
if(!Permission::check('ADMIN')){
if (!$this->ParentID) {
user_error('Cannot create new page at top level', E_USER_ERROR);
exit();
}
}
parent::onBeforeWrite();
}

I was unable to find the 'ParentID' field of the new page, or another way to check the page level, in the CanCreate method.
Then i created this code from different code examples and it worked!

Ps. I am a newbie in SilverStripe, dont know much about the programming part.