Initially I’m planning on having it outdoors at ground level using offcuts of wooden decking as a base. To expand where I plan though I’ll probably have to raise it to the level of the patios. I will move the large gravel aside to lay the decking then use a small gravel as ballast.I don't think that you have mentioned where this track will be placed. If outdoors, are you thinking ground level, built up on some sort of raised embankment or elevated? Indoors on the floor or on a baseboard? The location would affect the type of controls you want to use for the passing track.