If you need to get a ladder for a particular task, you might want to know more about ladders in general. This may help in your choosing the right ladder for the job. For many tasks, the rigid ladder is the type often used. Rigid ladders have many kinds – fixed, extension, step, platform step, and roof. The most basic of these is the fixed ladder; it has no moving parts. Extension ladders are composed of two ladders where one nests in the other for easy storage. Joined by a hinge at its top, and often forming an inverted V, are step ladders. If you need space to place things like paint cans, you might need a platform ladder, which has a platform at the top. Ladders that have hooks to firmly set them locked on the roof are called roof ladders. Aluminium is the choice material for many ladders, except those for electrical work.