They keep snow from sliding off tin roofs. They are used so that when the roof is ready to shed the snow all the snow doesn’t fall off the roof at one time. They are normally only used on tin roofs. Any roof with a rough surface doesn’t need them. Do not think you need to add them to your drawings.

I like it also. It gives the map a sense of depth. One thing you might consider is having two sets of symbols. The ones you used for the test image look great and work well with it but I know you want to show the texture in the symbols but please consider a textured and untextured set of symbols