Stylish: a modern day skillion and lean-to roof. Image by Bill Bradley, 2007 (Creative Commons License: Some Rights Reserved).
A lean-to roof is one of the most popular kinds of roofing types. In skillion form, it can be two shed roofs. One is usually taller than the other. The lesser of the two lean-to roofs may be a smaller structure. For example, the smaller one may be a conservatory backing onto a house with a shed roof.