there definetly should be an upgrade system and not a base exactly but the ability to make an outpost and upgrade into a base after a few upgrades or so. Like it would go from boarded up house to boarded house that has civilians ordered to help by guarding it and after making it a base you should be able to make like units from it but have a unit pop cap so you dont just completely make it unfair for the zombies + if you agree. This needs to be done.
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 "Class 3 Outbreak"){kind=icon}
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 "My zombie game test"){kind=icon}