A quick google came up with this.
http://www.momtastic.com/diy/128900-how ... om-mirror/
This is a fairly simple one. You can go quite fancy with all the different trims. Materials is less than 30 bucks.
I just go to homedepot for the trims/mouldings out of convenience.
You can avoid almost all mitre cuts by framing it like how windows are framed like this one. It can give you little shelf underneath the mirror as well.
B&T402 wrote:
This is a slightly more complicated task than four mitre cuts. I've seen this done applied over a bog standard plain builder's bath mirror (is that what op is looking at?) To make it pretty, you should use wide enough and thick enough material to apply flush to wall, and you need to remove the thickness of the mirror from the moulding with a router or table saw. Otherwise it looks like ass.
This is how I would do it but it might not be necessary. If the trim is nice straight sharp and thick, you won't notice it. You can also build up the trim from behind to overlap the mirror.
If the OP doesn't have the time, skill, or tools, then definitely ask a carpenter or a handy friend or family member.
The material for this job is extremely cheap.