Welcome aboard. I think I would model sectional shelf units, like modular, but not necessary to have any particular standard track spacings at the ends to work with other modules. That way you could make some industrial switching districts to play with. Later when the new building is built, these sections could be incorporated into the new space. I think that some time spent operating some switching layouts will give you a good idea of what sort of industries you want to incorporate in the new space. You will also discover what works and what doesn't. You might even find that what you built is really not what you want to run in the new layout and thus give you some better ideas of what you want to do in the new space. I think I would wait to build the yards until the new building was built. The size of your yards in combination with any hidden staging will determine the number and length of trains you can run. I think a yard built to fit in a relatively small bedroom, will be too small for the space you are planning in the new building. If the yards are big enough for the new building, they may be difficult to move out of the bedroom and overwhelm any layout you could put in the bedroom.
I think I would also reccomend that you just do scenery on the small straight shelf units and go around the corners of the bedroom with simple unscenicked curves to serve as connectors, unless you want to use the corners to practice scenery methods. I say this because the straight shelf units are relatively easy to fit into any layout space you would have available in the new building, but the curves might not fit as well. Also get your track working and switch layout the way you want it before doing a lot of scenery including ballast. That way you can easily move tracks around if you find that a different layout would work better.
I just found the forums today and thought I would join the group. I am not totally new to model railroading but I feel like it since it's been nearly 15 yrs since I have worked on a layout.
