The roll off roof was constructed out of the same materials as the rest of the building - 100 x 50 and 12mm ply. The tracks for the roof were made of 45mm x 45mm x 5mm angle iron. The running wheels were made from old fan belt pulleys salvaged from the local Auto Electrician - the centre was bored out and piece of nylon rod press fitted to make a bearing, this was itself bored out and the pullry wheel fitted between two pieces of angle iron and then bolted to the bottom support of the roof.

Not high tech but it works.