[Answered ]-Django. User adding items in model dropdown box

Then, this is a sign to have a separate model for building blocks:

class Material(models.Model):
    name = models.CharField(max_length=12, null=False)

You Location model would be related to the Material model. In case location can only have a single material, it would be a ForeignKey:

class Location(models.Model):
    materials = models.ForeignKey(Material)