I used 24mm goggle eyes and printed out a page of numbers that I cut out with my 1" punch. These fit perfectly over each eye. You are going to want to print your numbers out on Avery® Full-Sheet Sticker Labels. I tried printing mine on regular paper and then glueing them onto the goggle eyes but this doesn't work, they easily fall off once the "pressing" begins. You could also just use round sticker label and write the numbers on as suggested by Toddler Approved. When you have your numbers attached, hot glue them to a piece of cardboard.
I also made up and down buttons!
Using a large cardboard box, I left one end open to act as the elevator doors and the top flap to show the floor numbers. The arrow is attached on with a brad tack so that you can move it to different floor numbers.
Now let the fun begin!