This is a very good idea, specially if you take the opportunity to use the Arch module, and identify areas that could be enhanced
Indeed it would become an extremely precious resource...
Basically the whole idea of the Arch module is that: that after modeling your project, you can easily generate construction documents (plans, sections and facade views), quantities schedules (and thereafter price lists and construction timetables), and output your model for further, external work, such as structural calculations, energy calculations and renderings. Of course all this is still not working smoothly, but each of these operations is possible already.
There is no need to actually use the Arch tools to model your house, you can very well model everything with other tools (PartDesign, etc), and simply use the Arch module at the end to "qualify" the different objects (this is a wall, this is a window, etc..). Most Arch objects work either as modeling tools or as simple containers for other geometry. This is an important step in architecture modeling, which is the "semantics" (each object is not just a simple geometry, but is of a specific kind and has specific properties). This is what allows to easily query your model afterwards (give me everything that is in concrete, or give me all the floor area, all the walls, etc)
If you get the drawings from your friend in some 2D CAD format (dwg, dxf, etc), it'll be fairly easy to model on top of it (check the Arch tutorial
). If there is a 3D model already, even in mesh format, it's even better, but be aware that architecture models are not always very precise in their dimensions.