You could try an indoors run that can be folded up in a cooler (unheated) part of the house. You can contruct pretty cheap ones with cheap floorings from lots of materials.
Please don't do that if the difference in temperatures is too great and can cause illness. In this case, you have to get creative in the shed if possible!
what do you mean cause illness?
they are indoors at the moment!
Sorry - from the way you formulated it I assumed that your piggies were kept outdoors, and it would have caused problems if brought them into a fully heated house.
Quite a few members have indoors runs which can be stashed away when not needed. Perhaps you can do a search for "run" via our "search" function which you can find on the top bar for previous topics and ideas.