i want to give the users an option to add a new place if it doesn't exist
“Places” users can check in to have to be actual pages on Facebook with having the appropriate location data set. So what you want is basically to create a new Facebook page on the fly for your user to check in to.
This does not make much sense IMHO, because it would create just another “ghost” page with no actual useful info on it, not much action going on there at any foreseeable point in the future … so my advice would be: Don’t do it.
Instead, offer you users to check into any available places in their surrounding area – you can use the Graph API to search for those by lat/lon coordinates and a distance, see https://developers.facebook.com/docs/reference/api/#searching