although I have a 4m booth in the workshop, when we need to spray bigger stuff I made some MDF frames up, like face fix frames for a kitchen, 2 foot wide by 8 foot tall, installed some removable pin hinges to them and covered them in plastic to form a folding and storable extension, that you can then throw and tarp over and voila you have a bigger booth.
I have 8 spare frames already covered in plastic if you wanted them?