Building generation in a voxel engine

Well, consider making a "prefab" for a building. Think of it as painting the building in advance in a voxel editor that perhaps you have created. Then, when you want to instantiate a house, you can pick a spot at random and look for the nearest location where the house should be constructed. Just fill in the blocks with whatever the house would normally have, and ignore those that are nothing/air/void. Basically, you'll be "copypasting" in your "solids" of the building. The hard part is figuring out what a proper location is. Presumably where there are nothing above it (just sky) and presumably where all bottom layer tiles have contact with ground or it might end up balancing on a cliff.