You are going to cut out triangles that will cover the apex of each set of rafters.
													
																	How to notch out a 2x4 for a roof. 
									
	
		
	
																	So roughly 7 8 long for a 2 4. 
																	Layout your sheet of plywood on sawhorses. 
																	For the rafter to fit correctly you need to cut the bird s mouth exactly where the rafter will meet the wall. 
																	Access the roof using an extension ladder. 
															
													
									
	
		
	
																	For this example a section of roof is 20 feet wide. 
																	Measure out the span of your arch on a sheet of your plywood and cut a piece of string to the same length represented in the images as the line which connects a to b. 
																	The roof rafters provide integral structural support to the roof. 
																	Once you ve cut the top end of the first rafter you can calculate the position of the bird s mouth based on the height and width of the roof then use that rafter as a pattern to cut the others. 
															
													
									
	
		
	
																	Find the center point of your first measurement on the plywood and draw a line at a 90 degree angle from that center point until you reach the desired height of your arch. 
																	If you re framing a gable roof on a new house or building a shed or even a doghouse with a gable roof you ll need to cut a number of roof rafters. 
																	Birdsmouth joint how to cut a birdsmouth and how to cut and install roofing rafters and joists. 
																	This video will show you how to figure length and cut a common rafter for a gable roof using a framing square. 
															
													
									
	
		
	
																	Measure each section of the roof from side to side parallel to the line of the fascia board. 
																	Each side of the gusset will be 8 long but only 8 tall.