Someone has to teach the drone developers optimal brick laying techniques so they can program the drones. Every building site will no doubt need a handful of people to oversee the drones and verify their work. Also there will probably be several intricate nuances to complicated brick laying problems that will still require manual intervention. I wouldn't be surprised if at the end of the day a master bricklayer won't be able to use those drones far more efficiently and creatively than even the best drone programmer who has never actually held a trowel.