Slope is the rise over the run. In other words, the difference in y values divided by the difference in x values. Start at the bottom corner of the roof and count the tiles upwards until you get to the top tip of the roof. It should be 4. Now from that point, count over to the right until you are at the top. It should be 5.
It's not always easy to visualize this stuff. Do a Google image search for "3D Conic Sections" and take a look at a bunch of the results. That may help a bit. Let me know if you have any other questions.
