The layouts I make all have blocks put on top of the table. This allows me to lower the base altitude for rivers or small elevation changes that are smaller than a whole table. I make use of that method for the ferry and a small culvert.
Regarding the building with an interior, it rests on the outer edge of the layout on a corner so you get a cheese wedge look on the inside. The open doors and windows allow the user to assemble cars without having to move their view around to the side.