I'm inclined to think there are slanted surfaces everywhere you look. Next to me is a printer with a couple of slants, above. Down the street at the shopping center are sidewalk ramps, right.
And then there are the sloping roofs of houses and barns, lots of tilted roads and streets, fields that don't lie level, and a great variety of stairways. Including inclined surfaces in a drawing very often provides the spark that revives an otherwise comatose picture. Inclines sometimes bedevil the artist, but they're not so hard to do if (you guessed it) you start off with plain, old-fashioned linear perspective.
The simplest kind of incline is ...