The scale for this model will be approximately 1 foot to 200,000 light years. Of course, all these models can have a different scale than what is suggested here. At this size we should be able to fit the two major galaxies (the Milky Way and the Andromeda) into an average classroom at 11 feet away from each other. This model will entail hanging the various galaxies in a room so from this point on it will be referred to as an installation.
The students should be able to make up the various galaxies form the cotton batting. Refer to
for appropriate shapes and sizes. The Milky Way and Andromeda can be made up using the malleable wire bent into a pinwheel shape diameter of 1 foot as a substructure, much like the last model but on a much smaller scale. Then wrap the cotton around and tie with white thread to assimilate spiral galaxies.