I don't know if this helps anyone but the way I've found to get higher builders is to wait and not build anything till I get the dam part of technology and then set three builders each on the three projects. That is to say I set one to the broken down hut, one to building the other hut, and then one to the dam. If you put it on 1/2 speed then food doesn't go down as fast and then your workers can work and it will take longer by themselves meaning more construction points. It hasn't really gotten them to masters yet in my game but its getting them really close.