When I graduated college, I swore to myself that I would never hang something unframed on my walls again (the exception is inside closets). Luckily, my larger pieces of art came with frames, but the rest fell into two categories—small with interesting edges and everything else.
For small pieces on parchment or watercolor paper, I love a double glass frame. You get to enjoy every bit of it, and it makes it look rare and valuable.
For everything else, I am all about a custom mat. Here’s my rational. Standard size frames are pricy enough already, and spending an extra hundred bucks on a custom frame seems like money miss spent.
Find a standard frame that fits your art, with at least 2 inches of space between the edge of the art area (not the edge of the paper or poster) and the frame. I would normally try to give about 4 inches of space around the art, but every piece is different
Purchase a custom cut mat, in a color which complements the art and the frame. A colored mat is your chance to set your art apart.
I buy my mats from The Frame Destination because they seem to have a good variety of colors and the best prices, but there are many other sources on line. You could go into a store and have them measure and cut you a mat, but I’m not sure how competitive the prices are.
The cheapest large frames seem to be from IKEA, which makes custom mats even more helpful because IKEA frames are all wonky metric sizes.