The map was 18×24, so I cut the inside of the wood to be 17” on the sides and 23” on the top and bottom. That way the frame would cover a little bit of the map. I used them great tutorial for some guidance.
I put the sides together and glued them with wood glue. Then I used staples (lots of them!) to secure it. Since I don’t live by a hardware store I used what I had, but I would definitely buy some L brackets to make it more secure.****Update I used a staple gun with this but I would definitely use a nail gun instead of a staple gun to put it together****
I updated this and added another board, this is what it looks like now :). See it here.