This project is great for small & medium dogs. My Boston Terrier weighs 30 pounds and this works well for him. It obviously wouldn’t be strong enough for large, heavy dogs.
Start with small, solid, empty fabric bolts.
Stack some together until you get a satisfactory height. Then use a hot glue gun to glue each one together top to bottom and then glue each stack together front to back.
I just put the fabric over it and cut to fit.
I used Peanuts fleece to cover the top of the steps and gray fleece for the sides (I didn’t have enough Peanuts for the whole project). I used the glue gun for this, too, and it did fine without bleeding through the fabric.