I believe some of the buildings need repairs from time to time. If you drop your builder just in the right spot then they should repair the buildings and help to grow their skills.
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Vista™ Home Premium (6.0, Build 6000); AMD Athlon 64 X2 Dual Core Processor 4800+, ~2.5GHz; 1918MB RAM; DirectX 10; NVIDIA GeForce 6150SE nForce 430 128MB RAM; 1024 x 768 (32 bit) (75Hz)