If the distance from the roof to the ground is 20ft then you would need to use 40ft.
How to temporarily cover a hole in the roof.
One of the fastest and least expensive ways you can make a temporary emergency roof repair is to cover the involved area with a plastic tarp.
Really you don t want to be up on the roof in a storm trying to retrieve your flapping tarp.
Temporarily screw the rolled end down to the roof with at least two or three screws.
Of rope for each corner of your home.
Then fold the excess tarp under a few rotations for a tight clean fit.
A few holes in a roof that needs fixing anyway is pretty cheap insurance.
If you have a vent pipe in the way skip to step 5.
Make sure you get one that is large enough to cover the entire affected area and one that is meant to be used outdoors.
If available select a rope that will withstand various weather and is strong for securing your roof cover.
The most popular item used to cover a roof is a tarp.
Screw the 2 by 4 directly into the roof to secure it.
Pull the tarp tightly down onto the roof and smooth it out.
Use 1x2 along the perimeter of the tarp and a few nails or screws to hold them in place.
On the undamaged side wrap one end of the tarp around the 1 3 furring strip making sure the furring strip extends past each end by 1.