Things are built in the order you give the command. If you need a specific item built ahead of the queue, you don’t have to undo all the commands. Select a minion and right-click the specific items. You can tell them to “build this first.”
Set floors first. Minions move dramatically faster over the floor than on dirt. There is a movement penalty for dirt and for carrying materials as well. On top of that, flooring seems to negate the carrying penalty. Overall you will save huge amounts of building time if you set the floors first.
Minions will wall themselves in. Best to just plan for door positions ahead of time.
You can place a door on top of a built wall, and it’ll replace. What it doesn’t do is place a floor under the door. You’ll have to do so manually.
Light everything. Minions work faster in light and victims get scared in the dark.
Light can be blocked by objects, thus negating its benefits. A good example of this is the table and chairs for kitchens.
Tearing things down gives a full refund of all materials. So feel free to rebuild and experiment.