This is kind of hard to explain so bear with me. Normally you can not place stairs on the outside of a building so the top of the stairs is against the second floor wall. If there is not a first floor wall directly under the second floor wall you can. By placing stairs against the second floor wall the floor tile at the top of the stairs is now inside the building allowing you to clip through the wall without having to break it down. You can get onto the roof of the Muldraugh police station, Riverside Giga mart, Community center in March Ridge, Apartments in Rosewood, and several of the builds down town West Point. Basically anywhere the second floor over hangs the first. I have not tested this on player made buildings but im sure it would work. I also assume knocking down the first floor wall will allow you to then place stairs to clip through the second floor walls. The tile on the other side of the wall does have to be free from obstruction. This will not work if there is a chair or counter against the wall.