Two equally spaced straps running front to back and two side to side across the load will do the trick for most standard shaped items.
How to secure loads on a roof rack.
Step by step instructions step 1 packing step 2 secure everything well.
With the third option crossbars with side rails you can secure an item to the side rails and run tie downs from front to back securing them to the crossbars.
On each side of the roof you ll see a rack that runs the length of the roof of the vehicle.
Use a tie down that wraps around the item and the rails.
Ratchet straps are a cheap and easy way to ensure the highest level of safety when deciding how to secure items on a roof rack.
You can use a bungee cord to attach items together but do not use a bungee cord by itself to secure your load to the roof rack.