I bought a 36" x 24" thin board from Lowe's (approx $6) and used spray adhesive to attach the sign. If you use this method go slowly, start from one side and slowly smooth it out and spray a little at a time as you go. Engineer print paper is thin and can wrinkle or tear easy.
My favorite place to order engineer prints is Alpha Graphics. It only costs me $4 for a 36"x24" black and white print.
Here is another picture to help show the size.
You can purchase the digital printable PDF through my Etsy Shop, Party Crush Designs.