I googled it...

https://www.google.com/search?q=diy+framing+a+medicine+cabinet+mirror&newwindow=1&espv=2&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwjQ242P48rLAhVIvYMKHVivCo4QsAQIHw&biw=1600&bih=731

I found this link: http://www.hometalk.com/1150573/old-medicine-cabinet-gets-a-facelift-for-30

believe it or not I did Google quite a bit. By the way mine is recessed - not interested I don't THINK in adding a frame to a mirror door. Here for example is a ready-made fixed frame that Kohler makes for its Verdera line of med cabs: http://www.us.kohler.com/us/Poplin-Marabou-medicine-cabinet-surround,-40-wide/productDetail/vanities/991912.htm

How much space do you have between the cabinet and the wall? Did you look at Mirror Mates? I don't know how it works with multiple doors but you could take a look at this. I googled like crazy and didn't find much. I like the frame that Kohler has for the Verdera cabinet - nice simple lines. I was thinking of going that way but this only works with recessed mounted ones and ours will be surface mounted and none of the stains worked. I have been on the hunt for a framed med cabinet and it hasn't been easy finding one that meets my requirements. The back up plan is the tri-view verdera and the contractor making a frame like they have. I am looking at some cabinets this weekend and am hopeful that I will find one that works without having to go with the back up plan. I would just rather see the finished look and save that added time. What brand do you have? That compnay might have something.

Thx never had heard of them (http://www.mirrormate.com).

Don't know why you couldn't just go to frame shop if you have a recessed cab. Maybe it's that simple but still need to see more photos.

If you have some room between the cabinet and the wall you might be able to have someone make something like the Kohler one but you might have to nail it to the wall in sections. If you look around you can find some detailed drawings of this that would help someone see if it is possible to replicate the look. The back of the Kohler frame is thinner and the framing is a bit away from the cabinet to allow you to still open it.

Sofia has frames for their cabinets but you can also just get the chanel to put the frame around it. They might only sell that to go with their cabinets though. With the requirements for framing (minimum 1/2" rebbit) they gave me and what we needed, I wasn't finding much. If you want white or black you would have better luck. But I think a good carpenter (or talented hubbie) could probably do something like the Kohler one.

That frame simply underlaps the mounting flanges of the cabinet, and so I see why it's designed as it is. To use it, you have to put the frame in FIRST not afterwards. You'd have to have REALLY thick stiles / rails on the frame to impede cabinet door motion because of how the thicker parts (thin as they are) are set off slightly fro the perimeter of the unit. Also creates "aesthetic". And importantly you need a way for your finger to grab the edge of the door to open it. There are probably other ways to do it too (such as a way to avoid taking out the cabinet from its wall cavity -- build in place as you imply). This here hubbie can probably do it -- after a few mistakes, muttered profanities, return trips to the building supply store, etc. Oh and like so many things they are WAY overpriced for what they are!!

Here is a picture of one of my temporary ones that is now 4 years old. I wanted a Robern one that is about $1000 and did this with a cheap Kohler one that was $100 and maybe $20 worth of wood. And of course, I haven't installed the wall tiles because I haven't committed to a medicine cabinet yet.

(Sorry about the weird lighting. It's about to pour here and I still haven't installed my fan/light I bought a year ago:(