Roller doors are a low cost form of garage doors. Usually they are a continuous piece of rolled sheet steel than runs in tracks down each side of your garage door opening. The garage roller door rolls up into a small roll on an axle above the garage door opening. Roller doors can be manually operated easily using a spring assist mechanism or they can easily be automated using a Garage Door Opener.
A roller door is formed of rolled steel sheet welded along the edges and stacked on top of each other to give the roller door its height. There are corrugations rolled horizontally across the door to give the steel strength and sturdiness. Typically there is also bar attached to the bottom of the door called the bottom bar. This bottom bar should have a rubber weather seal on the bottom side to give your roller door a weather proof seal from the outside world. Your roller door should also contain a keylock that allows you to securely lock your garage and protect your valuables.
Typically roller doors are manufactured from pre-painted steel. They will usually come in a range of colours on the outside face and may just be finished in a 'grey' colour on the inside face.