I wanted to make my mom a large magnet board for her office, not a small one like you usually find. I went to the craft store and found magnet boards (four of them) and taped them together. I used scotch tape but duct tape would have probably been even better.
I found some wrapping paper that I liked and cut it out to be the same size. I put a very thin layer of Modge Podge on the front of the magnet board (the opposite side of the tape) and then laid my paper on top of it and smoothed it out. Make sure your Modge Podge layer is painted on very thin.
Next I found a frame the same size and took out the glass and replaced it with my magnet board (paper side facing out). I placed the glass on the back of the magnet board and then put the back of the frame back on.
Easy as that and you have a large magnet board!
Make sure you are careful, the magnet board is sharp and you can easily cut yourself. I did.