Then all you have to do to train a new builder is to drop a villager on one of the small huts to the left of the research table. Make sure that their action says, "Fixing hut" and watch them to see if they're successful. If they don't succeed, keep trying until they do. If their action says, "Examining hut" pick them up and try again - they won't get skill from that action. After they succeed at fixing the hut, they will have some building skill and will start fixing huts on their own. It will take awhile for them to develop to Master level, but they will eventually make it.
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Barbara
Unicorn
Last Day of Work