I did this for my daughter's room this week. Her wall are light purple and we wanted a dark purple chevron in between.
I knew I wanted the chevrons 8.5 inches wide/apart from each other so I simply cut a 8.5 inch square out of card board for my template.
Then working from ceiling to floor and marked it off and taped it.
I put tape scraps on the chevrons that would not get painted.
Then we painted 2 coats of the dark purple and this is how it turned out!