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. 
									
	
		
	
																	What types of tie downs work best. 
																	Another tie down material you should use is netting or a waterproof tarp. 
																	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. 
																	On each side of the roof you ll see a rack that runs the length of the roof of the vehicle.