The following Google Apps Script is designed to automatically close a Google Form once it has reached the number of responses you specify.
Do you ever create a Google Form and then forget to close it? Or maybe you want to limit the number of responses that a form can receive? If so, you can automatically close a Google Form once it has reached the number of responses you specify with this example Google Apps Script.
Source: The Gift of Script: Auto close Google Form after X responses
I use Google Apps Script to support staff and students in my job. I enjoy dabbling with creating tools to help with automation and I freely share my learning experiences on my blog, where I also have a number of useful Google Add-ons: www.pbainbridge.co.uk