"I went to the woods because I wished to live deliberately"    ........Henry David Thoreau

To draw a rafter in sketchup

1- To draw the rafter use the pen tool. Draw a line from the corner, down the top plate to the center (which is 60"). Then draw straight up 40" on the blue axis. Then draw the third line back to the start. This creates a triangle.
2- Erase the 40" vertical line. Then draw straight up 7 or 8 inches.  Go to the other end of the line and extend it (hover with the pen along the line and extend it 6". From the end of the extension draw straight up 7 or 8 inches (same distance you did earlier). Then connect to two vertical lines to create the line defining the top of the rafter.
3- Now use the push pull tool and make the rafter 4" thick.  Triple click and convert rafter to a component named rafter.
5- To create a roof surface, you can select the outside corners on one side which will form a coplaner rectangle. Use push pull and make 3" thick and you have a roof. You will have to fill in the center at the top.
4- Copy the component to the other side (outside to outside).
Now edit the rafter component (double click) and erase the line with the red circle in the drawing to the left.

If you now scale the component (choose center to center green boxes running horizontal) and move right side toward left. Let go of the mouse, enter -1 and hit enter. The second rafter should now be a mirror image of the original.

If this doesn't work for you, make a copy of the original, roatate 180 degrees and align it at the top. Then you can continue making copies so you have a total of six rafters.

Window Styles to be aware of