I made one that's 6ft x 4ft with a lid but it doesn't fold away or anything and just lives on its side in the garden with a plastic sheet over it, so no good for your requirements! However, here's a 6ft x 3ft one that folds down - it's still about 9ft of course but if you have a garage, you could easily slot it away down the side. Go to
www.diddly-di.fsnet.co.uk/contents.htm and down to the piggy care menu (first lot of green boxes) - click on 'outside run'. There are lots of pictures of it being made so it might give you some ideas for how to go about it, if nothing else!
Treen
www.treenspigs.com/index.html