If you create your own website, obviously you are the admin.
If you expect to get hired by someone as administrator, then you will need to have some experience to show how beneficial you can be as an admin.
You will need your "CV" updated with the latest sites you have worked for.
I have seen people creating websites where they offer their admin services among other things, like
seo consultancy, proofreading, etc.
Basically you need to build some authority/reputation around your skills.