We used to have a square folding run just 'off the peg' probs bought online. It did last pretty well for almost 10 years. The problem we had with it though was there were metal clips to bend over and secure the lid. After many uses, they sheared and the lid had to be balanced on top.
That would have been perfectly ok for pig safety, had we not got a dog that loves to eat pig poo! So, with the dog nosing at the sides of the run, this nudged in the folding side, causing the lid to fall in (no harm ever done as we knew the run wasnt safe enough to let the dog in the garden unsupervised with the run in that condition)
We just replaced the run last summer for a non fold one for dog security but we do miss the folding one for storage.
Our run was perfectly ok for a good 5 years I'm sure.