This is a 1989 film of a backyard roller coaster called The Termite. The ride starts off on the roof and then drops to ground level. If you search YouTube for backyard roller coaster there are a surprising number of people fiddling around with them. It is an odd hobby I wasn't aware of.
As you might expect, they've made some progress over the years. Below is a modern one called the Blue Flash that is motorized and features a loop.