If I were to re-do this project, I would make my frame first, then cut the cardboard to fit inside of it. Instead I made the canvases first, not knowing I'd want to make frames later. This made it a little more difficult to ensure the canvases would fit nicely inside of the frames, but I made it work.

What you'll need:

Large pieces of cardboard

Wrapping paper

Paint

Wood/MDF

Brad nail gun/liquid nails

Duct tape

Sawtooth hangers

Step 1: Cut cardboard to size

We had just gotten chairs for our living room so we had these large boxes. I cut them up to make two equal sized canvases. Because there were folds in my pieces, I used some duct tape along the folds to reinforce them (seen below).

You can also use plywood for this - but I didn't want to spend any more money than I had to.

Step 2: Wrap canvases

I took some old christmas wrapping paper and wrapped each piece of cardboard. I kept the print on the inside because the back of the paper was the plainer side. There was a grid on the back (to help with cutting straight lines), but I wasn't worried about it because my plan was to paint over it.

If you're using plywood, this step likely isn't necessary.

Step 3: Base coat

I painted the entire canvas white. Again, this was partially to cover up the grids on the back of my wrapping paper, but also because I wanted the background to be stark white.

Step 4: Paint your design

I went with these black semi circles, but you can do anything here! I first drew them out in pencil, then went over them with two coats of paint.

Edit: You can see above that there are some wrinkles in the paper. To get rid of these, after the paint dried, I flattened out the wrapping paper and repositioned the tape on the back of the canvases.

Step 5: Cut and paint your frame

Measure each side of your canvas and cut your wood to size. I used primed MDF but anything would work. Of course, the price will vary based on the material you choose. I chose to paint mine before assembling the frame, so I painted each piece black.

Again, if I were to re-do this project, I would have made the frames first, this way I could cut the cardboard to fit nicely inside. I thought it was a little more challenging to have to build the frames based on the size of the canvases.

Step 6: Assemble frame

I was going to miter the edges, but decided to keep this simple and just build a box. I connected the pieces with a some liquid nails and a brad nailer, but a hammer and nails would work just as well. I also secured a small piece in each corner, towards the back of the frame. This served as a reinforcement for the frame, and as an anchor for the canvases. I attached these pieces in the same way - liquid nails and a brad nailer. I also then painted them black, which I realized later was totally unnecessary :p

Step 7: Attach canvases to frames

I used some duct tape on each of the corner supports to attach the canvas to the frame. I didn't want to nail through my photo, and I didn't want anything too permanent incase I ever want to change it up.

(Optional) Step 8: Hang

To hang these frames, I took some sawtooth hangers off of an old frame I wasn't using at the moment, and screwed them into the back.

I was skeptical about pulling off this DIY, but I'm so happy with how they came out. These prints are over 4ft x 2ft each, and for less than $9 I really impressed myself with this one!