You should extend your " a bit" in PHP, SQL, Html and Css and after this youre maybe able to create your own CMS.
A CMS is only a solution to manage your contents on your site. Thats the reason why its called
Content
Management
System.
You should furthermore know that you´re not able to build your own cms within 24 hrs. It takes a lot of time and in some situations its much more useful to use cms from other users
Btw if you have your own cms you have to secure it too and for this you should know what you do.