A system for providing covers for surface areas of built structures; the system including a film of heat shrinkable material for stretching and heat shrinking over one or more of the surfaces of the built structure; the film formed as a sheet comprising an assembly of lengths of the heat shrinkable material prepared on a supporting surface; characterized in that the sheet is prepared by applying heat to overlap portions between adjoining lengths of the heat shrinkable material while the overlap portions are secured in contact between the supporting surface and a guide rail assembly laid over the overlap portions; the overlap portions welded together by a heat gun moveable along the guide rail assembly at a predetermined distance above the overlap portions. In a particular preferred form a kit is provided wherein adjacent lengths of the heat shrinkable material are spread on a supporting surface with a predetermined overlap of one length of the heat shrinkable material over the other; the guide rail assembly positioned over a first overlap portion of the overlap and the heat source moved along the guide rail assembly to weld the adjoining lengths along the first overlap portion.