In the description of Asyk's Command the Earth Path, he is able to raise up a castle by himself in a single scene, but is not able to do fine detailed work. So, assuming that the elementals can do the same, the rough body of the buildings should be in place, and with the assistance of other elementals and mortal craftsmen the walls can be polished and carved with appropriate murals showing the glorious tales of our wonderful gods doing wonderful things. That part of the construction will naturally take longer.