Here is a brief walkthough on ladders. For various tasks, the rigid ladder is the type often used. There are many types of rigid ladders, from the fixed type to the roof ladder type. The most basic of ladder types is the fixed ladder; it has no moving parts. Extension ladders are the type that can be lengthened, since one part is nested in the other for storage. The ones that form an inverted V are called step ladders. A platform step ladder has, because of its name, a platform at the top. Roof ladders have hooks that set them firmly hooked on the roof. Aluminium is the choice material for various ladders, except those for electrical work.