I would do half Hardened Clay (not stained) and half snow blocks for the spawn and it would have a two block wide cobblestone line running through the whole city, dividing summer and winter. Also, residents could not build things that were summery in the winter part, and vice versa, no wintery builds in the summer part. There would be a summer events area and winter events area in their respective districts, and a shop district in each area, and at the center of the spawn with the cobblestone line running through the middle have a tree that is made of half ice half flaming netherrack. I can provide you with a design for the tree if you wish, as it just so happens I have been experimenting what happens when ice and fire were put together, and I turned it into an experiential tree for Utopia, but seeing as the tree would be more fitting for your town's theme I am willing to give the design to you. Of course, you would have to join my nation first