This is a basic vinyl siding skill to learn - to cut 90° without marking it. It will save to time in the long run. In this case in wouldn’t make sense for me to set up a cutting table and go down a ladder just to cut a few pieces. Every installer will go through situations like this where it’s quicker to just cut a few pieces yourself than to call out a measurement and wait for the cut guy to cut it and get it to you. Many won’t agree with me but that’s ok. I’m just sharing my experience from ma