After trying various methods for construction,I think the best way for doign it is to define separate ConstructionProxy for each building. This gives maximum flexibility. Reading stuff from text files and using it for proxy setup is good for modding but has a lot of restrictions. If we change/add new parameters, the text file become obsolete. Also all the buildings must follow the same construction logic.
However if we define separate proxy BP for each building and specify which to use within the building class, we get alot of advantages. In most of the cases, all you need is to extend the MultiStageConstructionProxy BP and change its default values whcih define the various stages. But if you fancy it, you can override the functions (I will tell you which in a detailed tutorial soon) to get any kind of effect you want. For instance you can adjsut material properties along with the mesh change. Or use procedural stuff suing CustomMesh…
I am working on the tutorial as we speak and am also adding more detailed comments. I will push both into git within a week.