Really fun idea! I did encounter some bugs, notably that if you try to make a building, don't have enough resources, and then try to make a different building, it still won't let you because it checks the resource cost of the first building. This resulted sometimes in me making a different building than I intended. I also found that, after you get set up, the map is a little easy/turtle-heavy because the zombies seem to be the only thing that actively threatens you, so a lot of the high level upgrades didn't seem needed. I did have a lot of fun though, I found myself thinking of where to place my next buildings as if I were playing Civilization or something. Great work!