Decking?

They seem to have a natural eye for design being able to turn great balls of pulp into their magnificent chambered artworks. They don't seem too bothered at this time of year when you stick your head in their construction site.  I found it in the hedgerow. One attempted a stalk five times its length - managed to get airborne but gave up and resorted to shredding it before whisking it off in bits.  

I wonder which part of the house this is for.  I invited them to give us a hand but they were all on too much of a mission.