Best practise of re-modeling a building
That are certainly trade-offs between the two options.

I think main trade-off between the two options you described would be visual details vs. configurability.  

With a scanned design you have the ability to capture all the visual details that are in your hand crafted model.  Those same details might require more effort than you are willing to put into a CAD design (like window and door detail and other architectural accents).

The big disadvantage of a scanned model it that it would not be parametric so you can't fiddle with design details - like adjusting the width or spacing of the windows, the position of a door or external approach (stairs, etc).  Also you could play with the external skins/finishes and play with how wood looked as compared to concrete of brick. 

Another advantage of a CAD model would be that you would not be able to break out components and print them separately because of print volume issues or to be able to print in different colors. 

My personal preference would be to create a 3D Model using a CAD package.  The limitation on this would be that it might not have the same level of detail; but it would be much more flexible.  You could probably create the base design pretty easily either from the architectural drawings or by deconstructing the hand crafted model.  The model was probably built from pieces much the same way a 3D CAD model is created.

Here is a good example of how to do that.  In the example, they create a pretty detailed house design in Sketchup in 35 min by starting with scans of the architectural drawings.


There are quite a few other similar videos so you should look for the one that fits you best.