Well I know there is a way to make a custom tech tree but I can't find where buildings are dependent on others. For instance the Gateway needs the Nexus, but I want the Nexus to require the Gateway.
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The tech tree is done through requirements. So in the build ability for the probe there is an Info property which has all the buildings a probe can make. For each building (double click on a building) you can set a requirement for it.
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And requirements can be edited, of course.
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