At GardenLife Ltd. our walk-in runs are made from very strong galvanised 38mm tubular steel with a timber door frame. They are then covered in very strong 20 gauge hexagonal chicken wire mesh. (optional stronger 19g welded mesh upgrade)
We can supply runs with spans (across the door) of 2m, 3m, 4m or 6m and the depth of the runs can be almost any size. The biggest to date is 20m deep !