I found these patterns online. I don't know how crafty you are but I'm going to investigate to see how much it costs to buy the foam. You could make it to the exact dimensions you need and make it match your house! I think I'm going to eventually get this and make a ramp when my puppy is older. We'll see haha.. I don't have a lot of sewing experience.
Amazon.com: Simplicity 3906 Sew Pattern DOG BEDS...