Get your chalk reel.
How to snap a chalk line for roofing.
Hook the chalk line clip over the nail head or screw and reel out the string to the other end point along the straight surface.
Snap a vertical chalk line from the inside edge of the first shingle on the second row to the top of the roof and from the inside edge of the first shingle to the top of the roof.
3 tabs i snap the same baseline then square off that for a vertical bond line then i measure over half the width of a tab and snap a parallel line.
First snap a line for the top of the starter course whose bottom will be flush with the waterproof shingle underlayment wsu or felt underlayment which overhangs the drip edge by 1 2 inch.
If you have a well functioning chalk snap line you can slowly play out the line without.
But then i work on a 4 12 roof so you may have to use nails to hold the free end on your 9 12 roof.
Even small moisture amounts will cause chalk dust lines as well as any black or lead pencil marks to permanently damage steel surfaces.
Snap a chalk line the next time you need to mark a straight edge as part of a home improvement job.
Then hook one end of the chalk snap line to your beginning point.
The chalk will mark a straight line along the surface between the two points.
When it comes to the use of chalk near steel roofing and siding the following warning should have been added.
This saved on nail holes.
These chalk lines will serve as a guide for subsequent even numbered rows of shingles and odd numbered rows respectively.
Snap horizontal chalklines to help you keep the courses straight.
Then snap lines for every course or every other course.
First shake up the chalk inside your tool or add chalk if it does not have any.
I snap a line for every other course.
By bob vila using a chalk line is a quick way to give yourself a straight line as a building guide.
Once you have the chalk line over the second mark lift off the string and allow it to snap back onto the surface.
I snap chalk lines solo by wrapping the free end of the string on a brick and pulling tight on the other end.
I too am a diyer and not a professional roofer.