Derelict Sunday........Rusty Roof

I have seen this little construction in some fields where I sometimes walk, it intrigues me, as I can't imagine what it it's purpose would have been. It is long and very low, only the width of the sheet of corregated metal, and has obviously not been used for some considerable time..........., I wonder. ....... anyway a good subject for today's Derelict Sunday challenge.
Thank you everyone who has joined in this week, I shall be giving out hearts on Monday..........I am not sure there will be challenge next Sunday as it is Christmas day, depends on how many entries there are, maybe something in a humourous tone would be fun.......we still need a host for January please, I hope someone will volunteer, if not that will be the end of derelict Sunday......shame !