Restricting sharepoint site collection to a selected set of users/groups

1. Open Central administration

2. Click Application Management

3. Under application security, select Policy for web application

4.Go to the manage policy permission levels

5.click on the Add permission policy level

6.Here we can add our own permission policy level based on our requirement

7.give the name for new permission level (e.g. nositecreation)

8.select grant all option and select deny option for Create Subsite and Self-creation site

9.save it.

10.Come back to application manage policy

11. Go to the Add Users

12.Click on the next

13.Here we can add users/groups and under permissions select nositecreation

(which we created)