Guys,
I'll just throw this out here in case anyone has a situation that matches mine. I purchased two of these roundhouses used and pre-built. I do plan on having a detailed interiors so I wanted a somewhat realistic floor. So... I cut a base to fit the building (the original builder did not have things quite even), and I laid down 2 rail scale track with a middle rail using scale track spikes (no ties) right to the "concrete looking" base. It has worked flawlessly for several years now. You would need to be careful on the code you select has some light rail might not be high enough for O gauge wheels. In the end, I did not have to cut "fill in pieces" for the track to make the floor look complete.
