I found a couple of ideas for you

https://thefrugalhomemaker.com/2015/02/10/how-to-frame-out-that-builder-basic-bathroom-mirror-for-20-or-less/

https://www.youtube.com/watch?v=dU9cgAKKoSE

https://www.hometalk.com/5188887/q-framing-bathroom-mirrors

How to frame out that builder basic bathroom mirror (for $20 or less!)

https://thefrugalhomemaker.com/2015/02/10/how-to-frame-out-that-builder-basic-bathroom-mirror-for-20-or-less/

Hi Gayle, there are many posts on the Hometalk site from diy-ers who have framed their bathroom mirrors. Check out this link....

https://www.hometalk.com/search/all?filter=framing%20a%20bathroom%20mirror

I framed both my bathroom mirrors. One bathroom, I used straight cuts and medallion corners. The other bathroom I made mitre cuts. I used decorative molding. I spray painted the molding with Rustoleum on both sides. I used loctite power grab glue with painters tape and glued the molding right to the mirror. It has been many years and the frames still look brand new.

These are the two different types

Heres a great vid that may help you out.

https://www.youtube.com/watch?v=js7PgSJYDj0

I made a DIY frame for my mirror. I had Home Depot cut the wood for me, and I hung it with Command Strips! You can see my tutorial here: https://momhomeguide.com/diy-bathroom-mirror-one-room-challenge-week-4/

Here are some ideas: https://www.hometalk.com/search/posts?filter=frame%20mirror

Here is an idea. https://homeguides.sfgate.com/make-frame-directly-mirror-molding-93538.html

So many great suggestions here, hope you find the perfect solution. Its a project that I should think about.

How large is your mirror? There are many options.

Check out framemirror.com to see the kits they have. I have used them and they are great

Here’s how I did it: https://www.flippingtheflip.com/2019/12/how-to-diy-frame-wall-mounted-mirror.html?m=1

Hello, here is an easy frame to build,

https://www.youtube.com/watch?v=r29GGSXfMuU