Any time you build, invest, upgrade or collect your profits, you may see collectible items drop from buildings. Once you have all 3 items in a collection, you'll be able to hire a professional. Professionals are necessary to begin construction on many, many buildings. Mouse over any item in the Professionals menu to find out which building will provide it. If you're looking for a particular item, find its building type and begin contracts, and upgrades there, and even build more of the same type.
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