Drop Down choices from another table?

We are a manufacturer, and we're looking to track the materials used per job. We build custom closets, so each job could potentially have multiple rooms, each with a different material. I have created a table called "Layout" that we use to track the job as it passes through our engineering dept, and another table called "Materials" that would be used (it's new) to keep up with the different colors of board that we sell.

(I thought of this method instead of a list because I'd like to be able to update the materials through the years, i.e., if we change suppliers, etc., and potentially I might use this table in other relationships later on. If there's a better way, I'm open to it)

So my desire would be to create some drop-down options, so that the engineer could enter a room name, and choose a material from my table in a drop-down list. I currently have a relationship of one layout to many materials created. I can't seem to figure out how to pull in the list of materials by name into a drop down on my new layout form.