We had a doggy door in our last house. I think it was made by Petsafe, but I'm not sure. We got it at Lowes, and it was the XL. We had ordered a different brand at first, and had ordered one that went by the dog's weight. Thor weighed 100 lbs at the time and because his chest was so broad he wouldn't fit thru it. So we switched to the Petsafe. Ours went from a screened in porch to a deck that was a step lower. We installed it 4-5" off the floor of the porch. That way the dogs could reach it from the deck and it wasn't too low from the porch. Arabella was maybe 4-5 months old and was fine going in and out at that height, as well as Thor was. If it was going to a patio of the same height I think we would have put it a few inches higher. Arabella was fearless and was running in and out immediately, my other two took awhile to learn. I hope this helps.