Considering that my RR is linear as opposed to a flat table top of loops with open mid circle space, here are a few guide lines I follow for what ever the dimensions are:
Primarily RR support buildings.
No residential or non RR business buildings. Too much of a real estate foot print.
No square boxie cube structures. Too generic for me. Mfg cop out for sku control. If you have to see a label on the building to know what it is it is too "fits all" for me.
Essentially rectangular so as to demand minimum footprint between track(s) and platform edges or backdrop.
Preferably custom buildings picked up at train shows.
Scaled down building size from prototype can be very practical. Scale buildings and trees can dwarf any RR.
