This page is a WIP, as we are currently migrating our rules on this topic from our old campaign doc and choosing which things should go here vs on our campaign-specific site.
Material components gathered from a monster are sufficient for the creation of a single magic item, regardless of the monster's size. For example, one green dragon kill equals one potion of green dragon control.
DMG 117 lists the division for DMG scrolls, but UA does not provide a list for the scrolls it adds. Here is one that divides the protection scrolls between the two classes according to which class has the closest spell in their list: