so you could store player data into a database from Construct. This can be done using the AJAX object which can post data to a webpage. So if you want to simply store level against username you can post to a page called, submitlevel.php in which you handle the post data and add it to a database of level against username. Then on this secondary webpage you can use more php code to get the top 50 rows in the database when ordered by level and then display the data onto the page.
If you are unfamiliar with the AJAX object see here:
And for how to handle the data, w3schools has a good tutorial here: